fix(typeorm-codegen): avoid unused Column imports

[Boulea7]

Relates to #547.

Summary

• Avoid importing Column into scalar-only generated TypeORM models.
• Preserve Column imports for enum and JSONB-backed generated fields.

Validation

• node ../../common/scripts/install-run-rushx.js test -- codegen.test.ts — 49 passed.
• node ../../common/scripts/install-run-rushx.js test — 49 passed.
• node common/scripts/install-run-rush.js build --to @subsquid/typeorm-codegen — passed.
• node common/scripts/install-run-rush.js check — passed.
• node common/scripts/install-run-rush.js change --verify --target-branch origin/release/arrowsquid — passed.

Known limitations

• Repository-wide and scoped Biome checks report existing diagnostics in the touched legacy files; no unrelated formatting changes were made.
• rush test:lfs was not run; the local partial clone initially omitted 113 LFS fixtures.
• The full monorepo unit-test suite was not run.