fix(plpgsql-deparser): cursor SCROLL options, FETCH/MOVE directions, SQLSTATE conditions, bare RAISE, subscripted assignment targets

[pyramation]

Summary

Five round-trip corruption bugs found by fuzzing the deparser with esoteric PL/pgSQL (all outputs now reparse AND deploy against a real PG 18):

1. Wrong SCROLL bitmasks + wrong placement — deparseOpen tested cursor_options & 256/512 (those are CURSOR_OPT_FAST_PLAN/GENERIC_PLAN, which plpgsql always sets), so every OPEN c; became invalid OPEN SCROLL c;. Correct masks are 0x2/0x4, SCROLL goes after the cursor name, and only for unbound OPEN ... FOR — a bound cursor's option belongs on its declaration.
2. SCROLL dropped from cursor declarations — deparseVar never emitted it; now c SCROLL CURSOR FOR ... / NO SCROLL round-trip.
3. MOVE/FETCH directions lost or mangled — FORWARD n/BACKWARD n counts are stored as an expr the direction printer ignored (MOVE FORWARD 3 → MOVE); ALL is how_many = INT_MAX, not 0; and FIRST/LAST (ABSOLUTE ±1 with no expr) now print as FIRST/LAST so the reparse AST matches.
4. WHEN SQLSTATE '23503' deparsed as invalid WHEN 23503 — condnames matching /^[0-9A-Z]{5}$/ (named conditions are lowercase identifiers) are re-emitted as SQLSTATE 'xxxxx'.
5. Bare re-throw RAISE; deparsed as invalid RAISE EXCEPTION; — a raise with no condname/message/options is now emitted bare.
6. a[2] := 20 deparsed as invalid (a)[2] := 20 — the SQL deparser parenthesizes A_Indirection targets, but the plpgsql assignment grammar requires a bare identifier; deparseAssign unwraps a leading (ident) before [/..

Fixtures: Tests 47–53 in __fixtures__/plpgsql/plpgsql_deparser_fixes.sql (regenerated generated.json via pnpm fixtures), plus explicit snapshot tests in deparser-fixes.test.ts. Existing snapshot changes are all RAISE EXCEPTION; → RAISE; (fix #5). Full workspace suite passes.

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

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