Make Transport Struct Send/Sync

[chrsoo]

Priority: Low
Labels: technical-debt, area:networking, priority:low, async

Description:
Transport struct is not Send/Sync, limiting its use in async contexts.

Source: Item #100 from consolidated analysis
Files: Transport implementation

Acceptance Criteria:

• Transport implements Send
• Transport implements Sync
• Tests validate thread safety
• Documentation updated

Related Issues: None