add a non-static string variant for CustomError and InvalidParams

This enables uses cases that require error message built with runtime data such as
```
RPCError::InvalidParamsString(format!("Method {method_name} requires {num_required} params, got {num_actual}"))
```

```
// Forward error message
RPCError::CustomErrorString(1, err.what().to_string())
```

jsonrpc/src/error.rs

@@ -81,9 +81,15 @@ pub enum RPCError {
     #[error("Custom Error:  code: {0} msg: {1}")]
     CustomError(i32, &'static str),
 
+    #[error("Custom Error:  code: {0} msg: {1}")]
+    CustomErrorString(i32, String),
+
     #[error("Invalid Params: {0}")]
     InvalidParams(&'static str),
 
+    #[error("Invalid Params: {0}")]
+    InvalidParamsString(String),
+
     #[error("Invalid Request: {0}")]
     InvalidRequest(&'static str),
 

jsonrpc/src/message.rs

@@ -164,6 +164,11 @@ impl RPCError {
                 message: msg.to_string(),
                 data,
             },
+            RPCError::InvalidParamsString(msg) => Error {
+                code: INVALID_PARAMS_ERROR_CODE,
+                message: msg.to_string(),
+                data,
+            },
             RPCError::InvalidRequest(msg) => Error {
                 code: INVALID_REQUEST_ERROR_CODE,
                 message: msg.to_string(),
@@ -174,6 +179,11 @@ impl RPCError {
                 message: msg.to_string(),
                 data,
             },
+            RPCError::CustomErrorString(code, msg) => Error {
+                code: *code,
+                message: msg.to_string(),
+                data,
+            },
             RPCError::InternalError => Error {
                 code: INTERNAL_ERROR_CODE,
                 message: INTERNAL_ERROR_MSG.to_string(),