Implement debounce configuration

Follows similar pattern to recently added `throttle`

The integration test timing could lead to flakes but I tried to leave
a generous buffer to minimize this without making the test too long.

I wanted to add a second integration test for the debounce `timeout`,
but configuring debounce with a `timeout` seems to result in the
function never getting executed on the latest dev server (0.29.6). I
verified this is true with the JS SDK as well.

inngest-spring-boot-demo/src/main/java/com/inngest/springbootdemo/testfunctions/DebouncedFunction.java

@@ -0,0 +1,30 @@
+package com.inngest.springbootdemo.testfunctions;
+
+import com.inngest.FunctionContext;
+import com.inngest.InngestFunction;
+import com.inngest.InngestFunctionConfigBuilder;
+import com.inngest.Step;
+import org.jetbrains.annotations.NotNull;
+
+import java.time.Duration;
+
+public class DebouncedFunction extends InngestFunction {
+
+    @NotNull
+    @Override
+    public InngestFunctionConfigBuilder config(InngestFunctionConfigBuilder builder) {
+        return builder
+            .id("DebouncedFunction")
+            .name("Debounced Function")
+            .triggerEvent("test/debounced_2_second")
+            .debounce(Duration.ofSeconds(2));
+    }
+
+    private static int answer = 42;
+
+    @Override
+    public Integer execute(FunctionContext ctx, Step step) {
+        return step.run("result", () -> answer++, Integer.class);
+    }
+}
+

inngest-spring-boot-demo/src/test/java/com/inngest/springbootdemo/DebouncedFunctionIntegrationTest.java

@@ -0,0 +1,35 @@
+package com.inngest.springbootdemo;
+
+import com.inngest.Inngest;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.parallel.Execution;
+import org.junit.jupiter.api.parallel.ExecutionMode;
+import org.springframework.beans.factory.annotation.Autowired;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+@IntegrationTest
+@Execution(ExecutionMode.CONCURRENT)
+class DebouncedFunctionIntegrationTest {
+    @Autowired
+    private DevServerComponent devServer;
+
+    @Autowired
+    private Inngest client;
+
+    @Test
+    void testDebouncedFunctionExecutesTrailingEdge() throws Exception {
+        String firstEvent = InngestFunctionTestHelpers.sendEvent(client, "test/debounced_2_second").getIds()[0];
+        String secondEvent = InngestFunctionTestHelpers.sendEvent(client, "test/debounced_2_second").getIds()[0];
+
+        Thread.sleep(4000);
+
+        // With debouncing, the first event is skipped in favor of the second one because they were both sent within
+        // the debounce period of 2 seconds
+        assertEquals(0, devServer.runsByEvent(firstEvent).data.length);
+        RunEntry<Object> secondRun = devServer.runsByEvent(secondEvent).first();
+
+        assertEquals("Completed", secondRun.getStatus());
+        assertEquals(42, secondRun.getOutput());
+    }
+}

inngest-spring-boot-demo/src/test/java/com/inngest/springbootdemo/DemoTestConfiguration.java

@@ -24,6 +24,7 @@ protected HashMap<String, InngestFunction> functions() {
         addInngestFunction(functions, new InvokeFailureFunction());
         addInngestFunction(functions, new TryCatchRunFunction());
         addInngestFunction(functions, new ThrottledFunction());
+        addInngestFunction(functions, new DebouncedFunction());
 
         return functions;
     }

inngest/src/main/kotlin/com/inngest/Function.kt

@@ -81,6 +81,8 @@ internal class InternalFunctionConfig
         @Json(serializeNull = false)
         val throttle: Throttle? = null,
         @Json(serializeNull = false)
+        val debounce: Debounce? = null,
+        @Json(serializeNull = false)
         val batchEvents: BatchEvents? = null,
         val steps: Map<String, StepConfig>,
     )

inngest/src/main/kotlin/com/inngest/InngestFunctionConfigBuilder.kt

@@ -14,6 +14,7 @@ class InngestFunctionConfigBuilder {
     private var concurrency: MutableList<Concurrency>? = null
     private var retries = 3
     private var throttle: Throttle? = null
+    private var debounce: Debounce? = null
     private var batchEvents: BatchEvents? = null
 
     /**
@@ -147,6 +148,31 @@ class InngestFunctionConfigBuilder {
         burst: Int? = null,
     ): InngestFunctionConfigBuilder = apply { this.throttle = Throttle(limit, period, key, burst) }
 
+
+    /**
+     * Debounce delays functions for the `period` specified. If an event is sent,
+     * the function will not run until at least `period` has elapsed.
+     *
+     * If any new events are received that match the same debounce `key`, the
+     * function is rescheduled for another `period` delay, and the triggering
+     * event is replaced with the latest event received.
+     *
+     * See the [Debounce documentation](https://innge.st/debounce) for more
+     * information.
+     *
+     * @param period The period of time to delay after receiving the last trigger to run the function.
+     * @param key An optional key to use for debouncing.
+     * @param timeout The maximum time that a debounce can be extended before running.
+     * If events are continually received within the given period, a function
+     * will always run after the given timeout period.
+     */
+    @JvmOverloads
+    fun debounce(
+        period: Duration,
+        key: String? = null,
+        timeout: Duration? = null,
+    ): InngestFunctionConfigBuilder = apply { this.debounce = Debounce(period, key, timeout) }
+
     private fun buildSteps(serveUrl: String): Map<String, StepConfig> {
         val scheme = serveUrl.split("://")[0]
         return mapOf(
@@ -179,6 +205,7 @@ class InngestFunctionConfigBuilder {
                 triggers,
                 concurrency,
                 throttle,
+                debounce,
                 batchEvents,
                 steps = buildSteps(serverUrl),
             )
@@ -248,6 +275,20 @@ internal data class Throttle
         val burst: Int? = null,
     )
 
+internal data class Debounce
+    @JvmOverloads
+    constructor(
+        @KlaxonDuration
+        val period: Duration,
+
+        @Json(serializeNull = false)
+        val key: String? = null,
+
+        @Json(serializeNull = false)
+        @KlaxonDuration
+        val timeout: Duration? = null,
+    )
+
 internal data class BatchEvents
     @JvmOverloads
     constructor(