Fix untyped_args misreading keyword params as positional - #46

Summary

Redefiner.untyped_args (the path used when config.type_checking is false) decided positional-vs-keyword by checking param_proxy.position truthiness:

value = param_proxy.position ? args[param_proxy.position] : kwargs[param_proxy.name]

But keyword params also carry a non-nil .position (their ordinal position among all params, not just positional ones) — so a keyword-typed param like greeting: String gets misread as positional and looked up as args[position], which is empty for a keyword call. That reads as nil, which trips the "required but missing" check and raises Low::ArgumentTypeError — even with type checking supposedly disabled. This means type_checking = false is currently unusable for any class with keyword type expressions.

The working typed_methods path already decides this correctly, checking .type instead:

positional = %i[pos_req pos_opt].include?(param_proxy.type)

Fix

Use that same check in untyped_args instead of the position-truthiness check.

Verification

• Added #typed_kwarg to both type_checking_disabled/type_checking_enabled fixtures and mirrored the existing #typed_arg test cases for it.
• Confirmed the new tests actually catch the bug: stashed just the redefiner.rb fix and reran — 3 of the new tests fail with exactly the described Low::ArgumentTypeError, confirming they exercise the real bug rather than being incidentally green.
• Full suite: 147 examples (141 existing + 6 new), same 10 pre-existing failures as main (all Ruby-version-dependent formatting differences in hash/error-message output, unrelated to this change).