Capture the full per-overload SQL signature from CREATE FUNCTION

[estebanzimanyi]

The catalog carried only fragments of each function's SQL-facing signature — sqlArity (a count) and sqlReturnType (the return only). Without the concrete argument types, a binding generator cannot know which types a function is actually registered for, so it falls back to type-scope heuristics and over-registers. Example: minInstant/maxInstant are CREATE FUNCTION'd only for the ordered base types {tint,tbigint,tfloat,ttext}, but a generic "register over all temporal types" loop wrongly adds them for tbool and the geo types.

Change

Parse each CREATE FUNCTION statement statement-bounded (to its terminating ;) and attach, per @sqlfn name, the exact list of overload signatures:

sqlSignatures: [{args: [type, ...], ret: type}, ...]

A binding then emits one registration per signature over the concrete arg types — no type-scope heuristic. minInstant lands on exactly its four overloads; endInstant on all eighteen.

• Argument types are resolved mechanically, no hardcoded type list: a type vocabulary is gathered from the unambiguous positions (single-token bare args + every RETURNS clause), then each argument's type is the longest trailing run of tokens in that vocabulary — so a named argument (dist float, lowerInc boolean) yields its type, not its name.
• Statement-bounding also fixes return-type extraction: a LANGUAGE SQL default-arg overload (whose own AS 'SELECT ...' has no C symbol) could bleed its RETURNS across the ; into the next C-backed statement, corrupting 16 wrappers' sqlReturnType with fragments. That drops to 0.

Compatibility

sqlArity, sqlArityMax, sqlReturnType, sqlReturnTypeAll keep their existing meaning (now derived from the per-overload list), so current consumers are unaffected.

Verification

• minInstant/maxInstant → [tint,tbigint,tfloat,ttext]; endInstant → all 18 types; tintInst → [tint].
• 0 garbage in sqlSignatures and sqlReturnTypeAll (was 16).
• Full test suite green (156 passed, 8 skipped); regen clean against MobilityDB master 04398301c.