[Go] Add thread-safe serialization support for concurrent use

[chaokunyang]

Feature Request

No response

Is your feature request related to a problem? Please describe

The current Fory instance is not thread-safe, requiring users to:

• Manually manage Fory instances per goroutine
• Implement their own pooling for performance
• Risk data races if sharing instances

Describe the solution you'd like

Create a new fory/threadsafe package that:

• Wraps Fory instances using sync.Pool for zero-contention concurrency
• Provides the same API surface as the main package
• Automatically manages instance lifecycle (acquire/release)
• Includes both generic and non-generic APIs

Benefits

• Safe concurrent use out of the box
• Efficient pooling with automatic cleanup
• No performance overhead for single-threaded use (still use main package)
• Easy migration path for concurrent applications

Describe alternatives you've considered

No response

Additional context

No response