fix issue120 and issue103: add mutex to prevent data race in websocket write message and use named return values for WritePkg method

[No-SilverBullet]

What this PR does:

based on doc: https://pkg.go.dev/github.com/gorilla/websocket#hdr-Concurrency and https://github.com/apache/dubbo-getty/issues/120

1.add lock (sync.Mutex) in gettyWSConn struct

2. add new function 'threadSafeWriteMessage' to ensure that only one thread can send a message at a time,preventing race conditions.

based on https://github.com/apache/dubbo-getty/issues/103

3. use named return values for WritePkg method to return the captured panic to caller, which can prevent the panic in caller. Which issue(s) this PR fixes:

   Fixes https://github.com/apache/dubbo-getty/issues/120, https://github.com/apache/dubbo-getty/issues/103

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

NONE

[AlexStocks]

@No-SilverBullet good job. Maybe u can also check the tcp write is thread safe or not. refer issue https://github.com/apache/dubbo-getty/issues/103

[No-SilverBullet]

Should we use the packetLock in the session?

Based on this issue120 and document（ https://pkg.go.dev/github.com/gorilla/websocket#hdr-Concurrency

）, the writeMessage function in gorrila package is not concurrency safe, so a lock is added to prevent race conditions.

[No-SilverBullet]

@No-SilverBullet good job. Maybe u can also check the tcp write is thread safe or not. refer issue #103

ok

[No-SilverBullet]

Should we use the packetLock in the session?

Based on this issue120 and document（ https://pkg.go.dev/github.com/gorilla/websocket#hdr-Concurrency

）, the writeMessage function in gorrila package is not concurrency safe, so a lock is added to prevent race conditions.