fix(replication): decode MinIO metrics wire format

[cxymds]

Fixes rustfs/backlog#2098

Summary

• decode the complete MinIO-compatible replication metrics v1 wire shape into the existing stable ReplicationMetrics model while retaining the legacy snake_case decoder
• validate integer-valued counters directly from borrowed raw JSON tokens, avoiding f64 rounding and per-counter allocation
• map timed failures from failed.totals, accept compatible queued.peak/queued.max forms, preserve unknown extensions, and mark unavailable latency explicitly
• keep the output-v3 structure unchanged and preserve the pre-deserialization 8 MiB response bound
• sanitize replication extension keys and values without quadratic collision handling

Compatibility and performance

• one bounded response read followed by one explicit envelope parse; no untagged backtracking or whole-response Value DOM
• serde_json enables only raw_value; ordinary workspace float parsing is unchanged
• integer JSON tokens retain the full u64 range, while decimal/exponent tokens are converted exactly and fail closed on negative, fractional, non-number, underflowing, or overflowing values
• limitInBits follows the minio-go wire semantics of bytes per second
• MinIO wire omissions normalize to zero only for fields declared optional by the upstream contract; core discriminator and queue fields remain required
• legacy serialization, human output, and output-v3 schema remain stable

Test evidence

• red baseline: the captured RustFS fixture failed on main with missing field stats
• captured 1-object / 20-byte RustFS response fixture plus legacy, omitempty, timed failure, peak/max, mixed-shape, unknown-extension, and exact numeric-boundary tests
• signed mock Admin endpoint tests, including credential sanitization and declared/chunked 8 MiB overflow rejection
• process-level human and JSON rc bucket replication status tests; JSON is validated against schemas/output_v3.json
• two independent post-implementation expert reviews: approved for correctness, compatibility, and performance

Commands completed locally:

cargo fmt --all --check
cargo clippy --workspace --all-targets -- -D warnings
cargo test --workspace

All completed with zero failures. A real RustFS black-box rerun will be attached after the PR artifact is available.