fix: harden transport fallback and UBSHM validation

[Spicy-cream]

Summary

Address the latest review feedback on apache/brpc3535.

Changes

• Avoid wrapping an inherited AdapterConnect more than once for pooled and short connections.
• Unwrap inherited handshake connectors when a client-side high-speed upgrade is unavailable.
• Publish TCP fallback for the client-side no-upgrade path.
• Release RDMA and UBSHM resources immediately after server-handshake failure.
• Reject unterminated UBSHM shared-memory names before resource allocation.
• Add regression tests for connector wrapping, unavailable client upgrades, and malformed UBSHM names.

Validation

• Build: passed.
• Common transport handshake tests: 22/22 passed.
• UBSHM/UBRING tests: 16/16 passed.
• RDMA tests: 86/86 passed.

This PR targets the source branch used by apache/brpc3535.