feat: add TTS request reporting metrics

[YiminW]

Summary

• add common TTS request-level metrics and an empty final marker
• report HTTP vendor attempts with request bytes derived from output characters
• flush cached reporting on input end, flush, or fallback request ID changes
• preserve the existing interleaved-request buffering and TTS state behavior
• merge vendor metadata before final redaction
• keep masking idempotent and behaviorally aligned across Python and Go
• precompile the masked-value recognizers and guard them by canonical output length
• bump ten_ai_base from 0.7.57 to 0.7.58

Testing

• uv run pytest --noconftest tests/test_tts2_http.py -q (13 passed)
• Python utility tests in the TEN Linux container (54 passed)
• go test ./...
• go test -run "^$" -bench "^BenchmarkMaskSecret$" ./tests (~179 ns/op on Apple M4)
• modified Python files compile successfully