fix(plpgsql-deparser): fix 2 more failing fixtures (189/190 now pass)

[pyramation]

fix(plpgsql-deparser): fix 2 more failing fixtures (189/190 now pass)

Summary

This PR fixes 2 of the 3 remaining failing round-trip test fixtures, bringing the pass rate from 187/190 to 189/190.

Fixes:

1. Cursor declaration syntax - Output cursor_name CURSOR FOR query instead of cursor_name refcursor CURSOR FOR query (fixes plpgsql_transaction-17.sql)
2. Label placement - Output block labels before DECLARE section instead of between DECLARE and BEGIN (fixes plpgsql_control-15.sql)
3. Tagged dollar quote handling - Test utils now properly handle $tag$ delimiters, not just $$
4. Qualified variable names - Preserve block-qualified references like lbl.a in FOR loops

Remaining failure: plpgsql_varprops-13.sql - nested DECLARE inside FOR loop (variables are hoisted to top-level DECLARE, changing semantics)

Review & Testing Checklist for Human

• Verify cursor declaration syntax is correct for various cursor types (explicit cursors, bound cursors, etc.)
• Test labeled blocks with DECLARE sections to ensure labels appear in correct position
• Check that the skipLabel parameter doesn't affect nested blocks that should still have their own labels

Test Plan

cd packages/plpgsql-deparser
npm test

Verify output shows "Round-trip tested 189 of 190 fixtures (1 known failures skipped)"

Notes

• The escapedTag variable in extractBodyFromSql is computed but not used - this is harmless dead code
• Link to Devin run: https://app.devin.ai/sessions/8e1c971e9b194cd9a7dda034c89bd74b
• Requested by: @pyramation

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