feat(grammar): declaration attributes and cursors in procedural bodies

[sebsnyk]

Stacked PR, converted to draft. This sits third in the order #371 -> #372 -> #373 -> #374 and depends on #372. GitHub cannot base a fork PR on another fork branch, so the diff below includes the predecessors; only the last commit (609e422) is this change. It is not ready for review until #371 and #372 land and it is rebased; closing it until then is a reasonable call.

Problem

Declarations and cursors are where PL/SQL sources fail first, and they are common in PL/pgSQL too: v employees.salary%type, l_row employees%rowtype, c constant int := 3, n int not null default 0, arg alias for $1, cursor c is select ..., open / fetch ... into / close. Oracle's HR sample schema declares every procedure parameter with %type, so none of its procedures parse past the signature. Against real sources:

source	ERROR nodes with #372	with this PR
PostgreSQL src/test/regress/sql/plpgsql.sql	414	363
pg_partman sql/functions/check_default.sql	11	9
utPLSQL source/core/ut_utils.pkb	233	233

utPLSQL does not move because it needs Oracle's IS ... END name; header shape and package bodies, which are the next PR.

Solution

• type_attribute: object_reference % (TYPE | ROWTYPE), accepted wherever a declaration or a function argument takes a type. It is a separate alternative next to _type rather than an addition to _type itself, so column definitions and casts are untouched.
• function_declaration accepts CONSTANT, NOT NULL, and = / DEFAULT as well as :=; a second form covers name ALIAS FOR $n | name. The initialiser itself is unchanged (a parenthesised statement or a literal); allowing any expression there changes the tree of an existing test and is left for a separate PR.
• cursor_declaration: name [NO SCROLL | SCROLL] CURSOR [(args)] [RETURN type] (FOR | IS) query, and the PL/SQL word order CURSOR name .... Cursor parameters reuse function_arguments.
• open_statement, fetch_statement, move_statement, close_statement in grammar/statements/cursors.js, with the PL/pgSQL directions (NEXT, PRIOR, FIRST, LAST, ABSOLUTE n, RELATIVE n, FORWARD, BACKWARD) and OPEN c FOR query for cursor variables. OPEN c FOR EXECUTE ... comes with dynamic SQL in the next PR.
• The DECLARE section is one hidden rule (_declare_section) shared by function_body, procedure_body and block; the tree is unchanged.

One resolution worth a look: in FETCH ABSOLUTE n IN cur, the count is followed by IN, which is also the start of expr IN (...). The direction rule is prec.left so the count reduces first.

Notes

• tree-sitter test: 531 corpus tests on feat(grammar): RAISE, ASSERT, EXCEPTION handlers and GET DIAGNOSTICS #372, 538 with this PR (4 new in test/corpus/declarations.txt, 3 in test/corpus/cursors.txt), plus the 2 highlight tests. No ERROR/MISSING; scripts/test-keywords.sh passes.
• Parse table: STATE_COUNT 31012 → 31202 (+0.6% on top of feat(grammar): RAISE, ASSERT, EXCEPTION handlers and GET DIAGNOSTICS #372; +1.9% over main), parser.c 42.5 MB → 42.7 MB.