test: PostgreSQL driver conformance + benchmark vs pgx

[FumingPower3925]

Summary

Comprehensive conformance tests and performance benchmarks for the celeris PostgreSQL driver. Tests validate correctness against a real PostgreSQL instance. Benchmarks compare against pgx (the fastest pure-Go PG driver).

Conformance Tests

Connection & Auth

• MD5 authentication
• SCRAM-SHA-256 authentication
• Trust authentication
• Connection with all DSN formats (URL and key=value)
• SSL/TLS connection (if supported)

Query Execution

• Simple query: SELECT, INSERT, UPDATE, DELETE
• Extended query: prepared statements with parameters
• Multiple result sets from single query
• NULL handling (NULL params, NULL results)
• All supported types: int, float, bool, text, bytea, timestamp, date, uuid, jsonb, arrays
• Large result sets (100K+ rows)
• Empty result sets

Transactions

• BEGIN/COMMIT/ROLLBACK
• Isolation levels: ReadCommitted, RepeatableRead, Serializable
• Savepoints (if supported)
• Transaction rollback on error

COPY

• COPY IN with text format
• COPY IN with binary format
• COPY OUT
• COPY with large datasets (1M+ rows)
• COPY abort (CopyFail)

Error Handling

• SQL syntax errors
• Constraint violations (unique, foreign key, check)
• Connection loss during query
• Context cancellation during query
• Context cancellation during COPY

Pool

• Worker affinity routing
• Overflow to shared pool
• MaxOpen enforcement
• Connection health checks
• Idle connection cleanup

Benchmarks

vs pgx Comparison

BenchmarkSimpleQuery/celeris
BenchmarkSimpleQuery/pgx
BenchmarkPreparedQuery/celeris
BenchmarkPreparedQuery/pgx
BenchmarkBulkInsert/celeris
BenchmarkBulkInsert/pgx
BenchmarkCopyIn/celeris
BenchmarkCopyIn/pgx
BenchmarkPoolGetRelease/celeris
BenchmarkPoolGetRelease/pgx
BenchmarkConcurrentQueries/celeris
BenchmarkConcurrentQueries/pgx

Metrics

• Queries per second
• Latency (p50, p99)
• Memory allocations per query
• Connection establishment time

Acceptance Criteria

• All conformance tests pass against PostgreSQL 15+
• Tests run in CI with PostgreSQL container
• Benchmark suite comparing against pgx
• Zero-alloc on common query hot path (verified by benchmarks)
• Pool tests validate worker affinity behavior
• COPY benchmarks with 1M+ rows

Dependencies

• Depends on 129 (database/sql Driver implementation)
• Depends on 130 (connection pool)