[release] 1.51.1 - Improvements for polling and failed requests (#340)

### Improvements
  - Optimizes adding items to failed requests queue
- Sends full checksum with initialize requests even if full user hash
doesn't match
  ### Fixes
  - Fixes polling requests to send sinceTime and hash





>Included In This Release
>- 07c4aa9 sroyal-statsig
>   - Set Since Time and Hash for Polling (#338)
>- 05afda9 sroyal-statsig
>   - Don't Require Full User Hash Match for Checksum (#337)
>- c86d744 andre-statsig
>   - Optimize adding items to the failed requests queue (#335)

Sources/Statsig/DeviceEnvironment.swift

@@ -7,7 +7,7 @@ struct DeviceEnvironment {
 
     static internal let deviceOS = PlatformCompatibility.deviceInfo.os
     static internal let sdkType: String = "ios-client"
-    static internal let sdkVersion: String = "1.51.0"
+    static internal let sdkVersion: String = "1.51.1"
 
     let lock = NSLock()
     var sessionID: String? { UUID().uuidString }

Statsig.podspec

@@ -1,7 +1,7 @@
 Pod::Spec.new do |spec|
 
   spec.name         = "Statsig"
-  spec.version      = "1.51.0"
+  spec.version      = "1.51.1"
   spec.summary      = "Statsig enables developers to ship code faster and more safely."
   spec.description  = <<-DESC
                    Statsig enables developers to ship code faster and more safely by providing: