Ensure MessageServer.ReqID is 8 byte aligned (#2346)

Atomic operations such as atomic.AddUint64 must operate on 64-bit aligned memory when running on 32-bit systems, otherwise a runtime will panic occur. This is a known issue in go and might be addressed in a future release, see golang/go#36606.

## Motivation
Using atomic.AddUint64 on non 64 bit aligned address on 32 bit systems results in a runtime panic. The solution is to guarantee the data it operates on is 64 bit aligned. This can be done by defining such fields as the first item in a struct. See #2336.

Closes #2336 

## Changes
Moving ReqID to the top of MessageServer guarantees 8 byte alignment. See https://go101.org/article/memory-layout.html section _The Alignment Requirement for 64-bit Word Atomic Operations_ for details on why this works.

## Test Plan
This was tested on a Raspberry Pi 4B (armv7l) and on linux x86_64 resulting in no breaking changes. 

## TODO
- [ ] Test changes

## DevOps Notes
- [x] This PR does not require configuration changes (e.g., environment variables, GitHub secrets, VM resources)
- [x] This PR does not affect public APIs
- [x] This PR does not rely on a new version of external services (PoET, elasticsearch, etc.)
- [x] This PR does not make changes to log messages (which monitoring infrastructure may rely on)


Co-authored-by: Nikita Kryuchkov <[email protected]>

Author: jacquesadit

p2p/server/msgserver.go

@@ -61,8 +61,7 @@ type ResponseHandlers struct {
 // MessageServer is a request-response multiplexer on top of the p2p layer. it provides a way to register
 // message types on top of a protocol and declare request and response handlers. it matches incoming responses to requests.
 type MessageServer struct {
-	log.Log
-	ReqID              uint64 //request id
+	ReqID              uint64 //request id (must be declared first to ensure 8 byte alignment on 32-bit systems, required by atomic operations)
 	name               string //server name
 	network            Service
 	pendMutex          sync.RWMutex
@@ -74,6 +73,7 @@ type MessageServer struct {
 	workerCount        sync.WaitGroup
 	workerLimiter      chan struct{}
 	exit               chan struct{}
+	log.Log
 }
 
 // Service is the subset of method used by MessageServer for p2p communications.