TLS Stream reusability

[vinniefalco]

TLS streams like OpenSSL and WolfSSL need to be able to establish new sessions without destroying the object after a session ends.

[sgerbino]

TLS stream reusability is fully supported in the current implementation. Both OpenSSL and WolfSSL backends allow re-establishing sessions without destroying the stream object:

• tls_stream::reset() explicitly clears session state while preserving I/O buffer allocations
• Calling handshake() on a previously-used stream performs an implicit reset automatically
• OpenSSL backend uses SSL_clear() for efficient in-place reset; WolfSSL frees and lazily recreates the SSL object at next handshake

Test coverage includes testReset(), testResetViaHandshake(), and testResetFuse() validating multiple consecutive TLS sessions on the same stream object.