feat(go/adbc): add context.Context support for uniform OpenTelemetry instrumentation

[zeroshade]

Summary

Implements context.Context support for all Go ADBC methods to enable uniform OpenTelemetry instrumentation, cancellation, and deadline propagation (addresses #2772).

• Add DatabaseContext, ConnectionContext, and StatementContext interfaces that mirror existing interfaces but require context.Context for all methods
• Add extension Context interfaces: PostInitOptionsContext, GetSetOptionsContext, ConnectionGetStatisticsContext, StatementExecuteSchemaContext
• Implement adapter functions (AsDatabaseContext, AsConnectionContext, AsStatementContext) to wrap non-context implementations for backward compatibility
• Add IngestStreamContext helper for context-aware bulk ingestion
• Comprehensive test suite (9 tests, all passing)

Changes

New Interfaces (go/adbc/adbc.go):

• DatabaseContext - Database with context support for all operations
• ConnectionContext - Connection with context support for all operations
• StatementContext - Statement with context support for all operations
• Extension interfaces with context support

Adapter Implementation (go/adbc/context_adapters.go):

• Three adapter types that wrap non-context implementations
• Proper nil handling and double-wrap prevention
• Context pass-through for methods that already accept context
• Clear documentation about context limitations for legacy methods

Tests (go/adbc/context_adapters_test.go):

• Comprehensive test coverage for all adapters
• Tests for error handling, nil handling, and context pass-through
• All tests passing with race detector

Documentation & Examples:

• Updated package documentation explaining Context interfaces
• Added IngestStreamContext helper function
• Example code demonstrating adapter usage

Migration Path

For Applications:

// Wrap existing Database to add context support
db := driver.NewDatabase(opts)
dbCtx := adbc.AsDatabaseContext(db)

ctx := context.Background()
conn, err := dbCtx.Open(ctx)

For Driver Implementers:

• Existing drivers work unchanged via adapters
• New drivers should implement Context interfaces directly
• Gradual migration supported - no breaking changes

Test Plan

• All adapter tests passing (9/9)
• Race detector: PASS
• Backward compatibility verified (existing tests unchanged)
• Documentation examples compile

Notes

This is the first step toward uniform OpenTelemetry support. Future work includes:

• Updating individual drivers to implement Context interfaces natively
• Adding context-aware tests to validation suite
• Enhanced tracing instrumentation using context propagation