fix: typos (#1567)

# Fix: Corrected typos in source and documentation files

## Changes
1. **Corrected typo in `mempool/cat/spec.md:78`**:
   - "reponse" corrected to "response".

2. **Corrected typo in `mempool/cat/spec.md:39`**:
   - "recieved" corrected to "received".

3. **Corrected typo in `rpc/client/mock/client.go:57`**:
   - "apporiate" corrected to "appropriate".

## Purpose
- Improved code and documentation accuracy by fixing typos.

rpc/client/mock/client.go

@@ -54,7 +54,7 @@ type Call struct {
 	Error    error
 }
 
-// GetResponse will generate the apporiate response for us, when
+// GetResponse will generate the appropriate response for us, when
 // using the Call struct to configure a Mock handler.
 //
 // When configuring a response, if only one of Response or Error is