fix(kernel): classify socket retries by operation

[MikiEEE]

Summary

• add operation-aware read/write retry classification for accept, receive, send, and TLS handshake operations
• preserve TLS want-read and want-write overrides across Unix and injected MicroPython kernels
• accept bytes-like send buffers and preserve memoryview slices without copying
• migrate SmallStream and the web demo away from ambiguous exception-only retry checks
• preserve errno-less MicroPython connect backpressure behavior

Review

Independent adversarial review found two medium issues in the initial implementation: remaining ambiguous demo retry sites and an errno-less MicroPython connect regression. Both were fixed and the targeted re-review approved. A separate critic pass found no remaining blocking issues.

Validation

• 130 unit tests passed
• focused socket, protocol-client, and kernel tests passed
• package, test, and demo compilation passed
• git diff --check passed
• local Pyright, coverage, and PEP 517 build tooling were unavailable; GitHub CI is authoritative for those gates

Residual risk

Injected MicroPython tests cannot replace on-device validation.

Closes #35