Parse Gerber command streams without dropping errors

[mfiumara]

Summary

• parse *-terminated Gerber commands even when a file does not put each command on its own line
• retain outer tokenizer/parser errors instead of silently dropping those command blocks
• add regression tests for compact same-line commands and retained malformed-command errors

Gerber line endings are formatting only; * terminates commands. The released parser can therefore lose valid commands in compact streams. The first commit is the focused tokenizer change from #25. The follow-up keeps every outer parse_line error in the returned document rather than losing it through iterator flattening.

This intentionally excludes #25's later breaking ErrorContext API change and single-digit G-code expansion.

Verification

• cargo fmt --all -- --check
• cargo clippy --all-targets --all-features -- -D warnings -A clippy::blocks_in_conditions (the allowed test lint predates this change)
• cargo test --all-features — 57 passed
• RateMyPCB compact/error mutation checks — 7 passed
• Ucamco local corpus — 32 files, 102,909 records, zero unaccounted errors

[hydra]

Hi, I downloaded your branch and applied to my local copy, all the tests pass ok.

I then updated the gerber-viewer to use my updated local copy, but it fails to parse many of the elements in the main demo.

here's what it should look like:

here's what it looks like with this PR.

You can see that many of the elements are missing.

log.txt

I attached the error log for you.

To me this indicates the changes in this PR break the parsing code in an unexpected way, for which we don't have a test for.

Please can you investigate and create a new test which covers the parsing failure?