compiler: Preserve matching sql table column types

[sjh9714]

Summary

Fixes #1960.

SQL table columns with an explicit type label equal to the column key, such as date: date, were compiled as if the type were implicit and ended up with an empty rendered type. This keeps matching explicit scalar labels while preserving empty types for implicit columns like id and map-only columns like created {constraint: primary_key}.

Changes

• Only blank matching SQL column types when the column has no explicit scalar label.
• Add a compiler regression test covering date: date, an implicit id, and a constraint-only column.

Testing

• go test ./d2compiler -run TestCompile/sql-column-type-matches-name -count=1 failed before the fix with expected: "date", actual: "".
• TESTDATA_ACCEPT=1 GOTOOLCHAIN=go1.25.0 go test ./d2compiler -run TestCompile/sql-column-type-matches-name -count=1
• GOTOOLCHAIN=go1.25.0 go test ./d2compiler -run TestCompile/sql-column-type-matches-name -count=1
• GOTOOLCHAIN=go1.25.0 go test ./e2etests -run TestE2E/stable/sql_table_tooltip_animated -count=1
• GOTOOLCHAIN=go1.25.0 go test ./d2compiler -run 'TestCompile/sql' -count=1
• GOTOOLCHAIN=go1.25.0 go test ./d2compiler -count=1
• git diff --check

Note: I used Codex while preparing this change, and I reviewed the final diff and ran the listed checks locally.