Refactor TS and JS generators to share common field generation logic

[Copilot]

ts_gen.py and js_gen.py had ~88 lines of duplicated field generation logic and identical type mappings.

Changes

• New shared module ts_js_base.py:

  • common_types / common_typed_array_methods: Shared type dictionaries
  • BaseFieldGen.generate(): Parameterized field generation accepting type dicts

• Refactored generators:

  • FieldTsGen and FieldJsGen now delegate to BaseFieldGen.generate()
  • Type mappings imported from shared module

# Before (duplicated in both files)
class FieldTsGen():
    @staticmethod
    def generate(field, packageName):
        # ~88 lines of logic
        ...

# After
class FieldTsGen():
    @staticmethod
    def generate(field, packageName):
        return BaseFieldGen.generate(
            field, packageName, ts_types, ts_typed_array_methods
        )

Generated output unchanged. All 74 tests pass.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Increase code reuse with ts and js gen </issue_title>
<issue_description></issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Increase code reuse with ts and js gen  #39

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.