Bug: `suggest_fix_for_error` counts braces inside string literals

[terasakisatoshi]

Summary

suggest_fix_for_error counts raw { and } characters in source_code when rustc reports an unclosed delimiter. This includes braces inside string literals, which produces misleading brace-balance suggestions.

Reproducer

using RustCall

stderr = "error: unclosed delimiter"
source = "fn foo() { let s = \"{\"; }"

RustCall.suggest_fix_for_error(stderr, source)

Actual output includes:

[
    "Mismatched braces. Check that all opening `{` have matching closing `}`.",
    "Found 1 more opening brace(s) than closing brace(s).",
]

Expected

The brace-count hint should ignore braces inside string literals and should not report an extra opening brace for this source.

Affected Code

• src/exceptions.jl:556-564

Notes

This is only diagnostic text, but it points users in the wrong direction during syntax debugging.

[terasakisatoshi]

Addressed on branch fix/issues-232-235 in local commit f721364.

Changes:

• replaced raw brace counting in suggest_fix_for_error with a scanner that ignores braces inside string literals
• added a regression test for "fn foo() { let s = \"{\"; }"

Verification:

• julia --project test/test_error_handling.jl
• `julia --project -e 'using Pkg; Pkg.test()'

[terasakisatoshi]

Closed via merged PR #236.