Filter global type overrides by engine before generating

[methakon]

Filter global type overrides by engine before generating

Fixes #4624.

A global override that sets engine was applied to every generated package, not just the one being generated.

opts.Parse prepends the global overrides to the per-package list, and goInnerType returns on the first match. So with postgresql, mysql and sqlite declared in one config, all three packages picked up whichever db_type: text rule was listed first, and all three took the last matching go_struct_tag.

Reproduced

Using the config from the report against bdbe55db:

engine	before	after	expected
postgresql	Value string / Code json.RawMessage, tag backend:"sqlite"	Value string / Code json.RawMessage, tag backend:"postgresql"	✅
mysql	Value string / Code json.RawMessage, tag backend:"sqlite"	Value sql.NullString / Code []byte, tag backend:"mysql"	✅
sqlite	Value string / Code json.RawMessage, tag backend:"sqlite"	Value []byte / Code string, tag backend:"sqlite"	✅

sqlc generate exits 0 in both cases, so the wrong types are silent.

The fix

parseGlobalOpts drops overrides whose engine is set to something other than the engine being generated. Overrides with no engine still apply everywhere, which is what single-engine configs rely on.

engine := req.Settings.GetEngine()
if engine != "" {
	filtered := make([]Override, 0, len(options.Overrides))
	for _, override := range options.Overrides {
		if override.Engine != "" && override.Engine != engine {
			continue
		}
		filtered = append(filtered, override)
	}
	options.Overrides = filtered
}

req.Settings.Engine is already what goInnerType switches on to pick the engine's own type mapping, so the selector is available at this point without any plumbing. The config layer already requires engine on global overrides whenever more than one engine is in use, so this filter never has to guess.

Tests

Adds internal/endtoend/testdata/overrides_global_engine, which generates three packages from a single config and pins every type and struct tag. Reverting options.go makes it fail with the sqlite types in all three packages:

- 		Value sql.NullString `backend:"mysql"`
+ 		Value string          `backend:"sqlite"`

go test ./internal/endtoend -run 'TestReplay/base' passes (251s), as do ./internal/codegen/golang/... and ./internal/config/.... gofmt and go vet are clean.