test: cover remaining parser branches

[omsherikar]

Exercise not_initialized token, module docstring rules, extern, primaries, and default var values .

Solves #43

[Copilot]

Pull request overview

Adds targeted tests to exercise previously uncovered/rare branches in src/arx/parser.py, improving parser coverage per issue #43.

Changes:

• Strengthens the local _parse() test helper with an AST type assertion.
• Adds parser branch tests for: leading not_initialized token handling, module docstring placement rules, top-level empty ; statements, extern prototypes, primary-expression edge cases, and default initializer values for typed var declarations without =.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

In test_parse_consumes_leading_not_initialized_token, resetting token_list.position and token_list.cur_tok is redundant (a freshly created TokenList from Lexer().lex() already starts at position 0 with cur_tok set to not_initialized), and mutating these internals makes the test more brittle than necessary. Consider removing these assignments and just prepend the not_initialized token (or build a new TokenList with the extra token) before calling Parser().parse().

Suggested change

	token_list.position = 0
	token_list.cur_tok = Token(TokenKind.not_initialized, "")