feat(harness): add granular benchmark phase metrics

[HayatoKanee]

Closes #853

Summary

• add granular per-phase benchmark telemetry for prover benchmarks
• record phase time, uploaded/downloaded bytes, and IO wait in CSV output
• add matching tracing instrumentation and shared telemetry contracts
• harden browser benchmark startup for proxied environments

What changed

• add stable benchmark phases for preprocess, handshake subphases, record-layer flush, finalization, and transcript proving
• extend harness metrics and CSV schema with flat phase_* columns
• upgrade the harness meter to track bytes plus read/write wait time
• wire telemetry through prover, MPC-TLS, and proving paths
• make browser executor startup more robust by fixing DevTools binding, adding startup/RPC timeouts, and bypassing proxies for local DevTools lookup

Validation

• cargo test -p tlsn-harness-core -p tlsn-harness-executor -p tlsn-mpc-tls -p tlsn --lib --no-fail-fast
• cargo test -p tlsn-harness-runner --no-run
• native benchmark smoke passed
• browser benchmark smoke passed
• native and browser CSV outputs both contain populated phase_* fields with identical headers

Example phase timings from the first cable sample:

Native

• phase_preprocess_setup_time_ms=13174
• phase_handshake_ke_online_time_ms=41
• phase_handshake_prf_session_keys_time_ms=162
• phase_handshake_record_setup_time_ms=21
• phase_handshake_prf_server_finished_time_ms=43
• phase_handshake_prf_client_finished_time_ms=43
• phase_record_layer_flush_time_ms=295
• phase_finalize_tls_auth_time_ms=54
• phase_prove_transcript_time_ms=415

Browser

• phase_preprocess_setup_time_ms=13609
• phase_handshake_ke_online_time_ms=96
• phase_handshake_prf_session_keys_time_ms=166
• phase_handshake_record_setup_time_ms=83
• phase_handshake_prf_server_finished_time_ms=54
• phase_handshake_prf_client_finished_time_ms=54
• phase_record_layer_flush_time_ms=474
• phase_finalize_tls_auth_time_ms=63
• phase_prove_transcript_time_ms=799

Notes

• phase metrics are emitted to CSV in this PR
• plot support remains coarse-only and is not changed here
• the example timings above are from smoke runs and are included to show the new output shape, not as stable performance claims