Refactor UDF server and external function type system

[kesmit13]

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[Copilot]

Copilot reviewed 15 out of 15 changed files in this pull request and generated no comments.

Comments suppressed due to low confidence (3)

singlestoredb/tests/test_ext_func.py:1150

• Renaming test functions to start with an underscore may cause them to be skipped by the test runner. Confirm if this change is intentional.

def _test_varchar_mult(self):

singlestoredb/functions/ext/asgi.py:271

• The indexing with out[0][0] to determine the length for row_ids may be unreliable if the structure of 'out' changes. Verify that this logic correctly reflects the number of result rows.

row_ids = array_cls([row_ids[0]] * len(out[0][0]))

accel.c:3920

• [nitpick] Verify that allowing NUMPY_FIXED_STRING along with NUMPY_OBJECT for character output types is correct according to the intended binary data handling.

if  (col_types[i].type != NUMPY_OBJECT && col_types[i].type != NUMPY_FIXED_STRING) {