Align Lua parser diagnostics and validate missing closers

[akeit0]

Malformed Lua diagnostics exposed enum names in the public AST parser, and the execution compiler narrowed reserved token IDs to char, producing messages such as ą expected. Both now use Lua keyword/punctuation spelling and token categories. For example, if true print() end reports 'then' expected near 'print', and local = 1 reports <name> expected near '='.

The public LuaSyntaxTree.Parse parser now reports the opening construct and its line when a closing token is missing on a later line: 'end' expected (to close 'do' at line 1) near <eof>. It rejects missing block/table closers that it previously accepted and handles valid multiline grouped expressions and table keys. EOF diagnostics use the lexer end position, including trailing newlines and comments, rather than the retained previous token.

The execution compiler already tracked opening constructs. Preserve its full int token IDs, quote expected punctuation, and use categories for expected names/numbers/strings. This fixes its diagnostics without changing valid execution behavior.

Follow the official Lua 5.2 lexer token2str/txtToken conventions and parser check_match behavior. The fixed syntax/category distinction also applies in 5.3 and 5.4. Public signatures remain compatible. AST string context still uses existing token display text, so this does not promise byte-for-byte diagnostic parity for original quote styles or long-bracket delimiter levels.

Fixes #113.

Validation:

• 71 new regression cases; ParserTests: 72 passed. Missing-token and missing-closer cases check both the execution compiler and public AST parser against explicit expected diagnostics. Also covers nested blocks, EOF/comment positions, valid multiline constructs, Turkish-culture category names, and preserved literal display.
• Runtime tests: 397 passed. Source generator tests: 24 passed.
• Release builds for netstandard2.1/net6.0/net8.0/net10.0: zero warnings/errors.
• CSharpier checks all 247 files; git diff check passes. Temporary verification files remain outside git.