Add duckdb support as optional

[bligneri]

Hi there,

I understand DuckDB support was removed due to CGo dependencies and binary size concerns.

Since I need DuckDB support for a few projects, I'm proposing a different approach: opt-in support via build tags. This means:

• Zero impact on default builds
• DuckDB is completely excluded unless explicitly built with the duckdb tag
• No CGo for regular users - the default goose binary remains CGo-free
• Flexible build options - users who need DuckDB can choose the variant that fits their needs

Build Options

Three Makefile targets are provided for DuckDB builds:

• make build-duckdb - full binary with debug symbols (~97MB)
• make build-duckdb-nodebug - stripped binary (~73MB)
• make build-duckdb-nodebug-compressed - UPX compressed (~18MB)

Binary Size Comparison (x86_64)

-rwxrwxr-x  1 ben ben  54M Oct 10 20:08 goose-default
-rwxrwxr-x  1 ben ben  37M Oct 10 20:22 goose-default-stripped
-rwxrwxr-x  1 ben ben  97M Oct 10 20:37 goose-duckdb
-rwxrwxr-x  1 ben ben  73M Oct 10 20:33 goose-duckdb-nodebug
-rwxrwxr-x  1 ben ben  18M Oct 10 20:30 goose-duckdb-nodebug-compressed
-rwxrwxr-x  1 ben ben 9.0M Oct 10 20:52 goose-nodebug-compressed

For the compression I used upx and the results are interesting for em.

Implementation

• DuckDB dialect implementation in internal/dialects/duckdb.go
• Build tag //go:build duckdb ensures opt-in only
• Integration tests included (make test-duckdb)
• Documentation updated in README.md

This approach allows DuckDB users to benefit from goose without impacting the default build for everyone else.

[mfridman]

When we get around to this, the Go driver (still CGO) moved to https://github.com/duckdb/duckdb-go