feat(connectors): add Google BigQuery sink connector

[kparisa]

Which issue does this PR address?

Closes #4393

Rationale

Streams Iggy messages into BigQuery through the Storage Write API _default stream with Arrow-encoded rows. Supports mapped and raw modes, Iggy metadata columns, per-row rejection with offset logging, request splitting below the AppendRows limit, and retries for transient gRPC failures. Verified against a live BigQuery table; CI coverage uses an in-process fake of tables.get and BigQueryWrite.

What changed?

New sink connector under /core/connectors/sinks

Local Execution

• Passed
• Pre-commit hooks ran

AI Usage

• Leveraged ChatGPT, Claude for planning, test scenarios, implementation.
• Ran local tests, publishing payloads to iggy, configured GCP test project, created the BigQuery (BQ) dataset "iggy" and events table.
• Verified the records in the BQ table.
• Tested failure scenarios as well for mis-configs and missing table definitions etc

[codecov]

Codecov Report

❌ Patch coverage is 89.29619% with 219 lines in your changes missing coverage. Please review.
✅ Project coverage is 87.86%. Comparing base (2d7fddb) to head (a32b3af).

Files with missing lines	Patch %	Lines
core/connectors/sinks/bigquery_sink/src/encode.rs	91.83%	43 Missing and 32 partials ⚠️
core/connectors/sinks/bigquery_sink/src/client.rs	74.60%	55 Missing and 10 partials ⚠️
core/connectors/sinks/bigquery_sink/src/schema.rs	90.68%	37 Missing and 4 partials ⚠️
core/connectors/sinks/bigquery_sink/src/sink.rs	79.31%	20 Missing and 4 partials ⚠️
core/connectors/sinks/bigquery_sink/src/lib.rs	96.34%	4 Missing and 4 partials ⚠️
core/connectors/sinks/bigquery_sink/src/error.rs	93.81%	4 Missing and 2 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #4394      +/-   ##
============================================
- Coverage     87.96%   87.86%   -0.11%     
+ Complexity     1579     1578       -1     
============================================
  Files          1290     1296       +6     
  Lines        230145   232191    +2046     
  Branches     193480   195529    +2049     
============================================
+ Hits         202440   204007    +1567     
- Misses        22980    23367     +387     
- Partials       4725     4817      +92     

Components	Coverage Δ
Rust Core	89.04% <89.29%> (-0.03%)	⬇️
Java SDK	68.72% <ø> (-0.02%)	⬇️
C# SDK	77.61% <ø> (-0.02%)	⬇️
Python SDK	91.24% <ø> (ø)
PHP SDK	85.67% <ø> (ø)
Node SDK	94.91% <ø> (-1.69%)	⬇️
Go SDK	70.29% <ø> (+0.10%)	⬆️

Files with missing lines	Coverage Δ
core/connectors/sinks/bigquery_sink/src/error.rs	93.81% <93.81%> (ø)
core/connectors/sinks/bigquery_sink/src/lib.rs	96.34% <96.34%> (ø)
core/connectors/sinks/bigquery_sink/src/sink.rs	79.31% <79.31%> (ø)
core/connectors/sinks/bigquery_sink/src/schema.rs	90.68% <90.68%> (ø)
core/connectors/sinks/bigquery_sink/src/client.rs	74.60% <74.60%> (ø)
core/connectors/sinks/bigquery_sink/src/encode.rs	91.83% <91.83%> (ø)

... and 43 files with indirect coverage changes

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[hubcio]

/skill team-review-slim

[github-actions]

Summary: The review found a rustdoc link error that fails the doctest job, a token error classified as permanent so open() never retries it, a missing integration test, and hot-path encoding costs. Two simplifications cover a hand-rolled hex helper and two Option fields that always move together.

Counts: critical 0, warning 5, nit 2, simplification 2

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This review was generated by Claude Code 2.1.284 on deepseek-flash[1m]. Review the output before you act on it.