fix(plpgsql-parser): multi-function scripts no longer all get the first function's body

[pyramation]

Summary

In plpgsql-parser, a script with multiple LANGUAGE plpgsql functions deparsed every function with the FIRST function's body:

CREATE FUNCTION f1() ... $$ BEGIN RAISE NOTICE 'one'; END $$ ...;
CREATE FUNCTION f2() ... $$ BEGIN RAISE NOTICE 'two'; END $$ ...;
-- transformSync output: both bodies were 'one'

Root cause: extractFunctionInfo called parsePlPgSQLSync(fullSql) — the whole script — so each ParsedFunction.plpgsql.raw contained ALL functions, and deparse/deparseSync pair each statement with plpgsql_funcs?.[0], i.e. always the first.

Fix in parse(): slice each statement's own SQL from the source using rawStmt.stmt_location/stmt_len (byte offsets, via Buffer) and pass only that to parsePlPgSQLSync, so plpgsql_funcs has exactly one entry per function and the existing [0] pairing is correct.

Tests: transform round-trip asserting each of three functions (incl. a trigger fn) keeps its own body exactly once, and a parse()-level test asserting functions[i].plpgsql.raw contains only its own function's AST. Full workspace suite passes.

This was the bug noted in constructive-db's kitchen-sink fixture ("multiple PL/pgSQL functions in one file all receive the first function's body"), which forced its transform fixtures into a single comprehensive function.

Link to Devin session: https://app.devin.ai/sessions/eeb8deba0c04475091df703c88877302
Requested by: @pyramation

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