feat: [influxdb] v3 support — http + flight sql + flux fixes

[crandles]

Description

Closes #984.

• v3 HTTP SQL + InfluxQL via /api/v3/*, json/jsonl/csv response formats, /api/v3/write_lp passthrough
• Flight SQL (gRPC) proxy: per-backend flight_port, IPC-byte cache, header forwarding, daemon shutdown + SIGHUP reload
• Flight SQL metadata RPCs (Tables, Catalogs, Schemas, TableTypes, SqlInfo) and prepared-statement lifecycle (Create/Execute/Close/DoPut), cache key includes bound-param hash
• SQL parser handles both date_bin() and date_trunc() bucketing
• Flux: now() in range(), balanced-paren tokenization for nested calls, multi-table CSV reads — was silently falling through to HTTPProxy on common Grafana shapes
• Dev env: influxdb3 compose service + side-by-side dashboard exercising metadata RPCs; verify-influxdb3.sh for direct HTTP SQL

InfluxDB 3 Core 3.10 returns a parameter schema at prepare time but doesn't resolve bound values during planning ("No value found for placeholder"). Parameterized prepared statements fail at the upstream, not the proxy; integration test for that path omitted pending upstream fix.

Follow-ups:

• refactor Flight listener to use feat: [clickhouse] native binary protocol + parser + grafana v4 plugin #981's ProtocolListener once that merges

Type of Change

• • Bug fix
• • New feature
• • Test coverage
• • Documentation

AI Disclosure

• • This contribution DOES include AI-generated changes, and I have reviewed the relevant contributing guidelines.