Support UTF-8 and ISO-8859-1 source files

[floze-the-genius]

Summary

• read HDL source bytes as UTF-8 when valid
• fall back to byte-preserving ISO-8859-1 decoding when UTF-8 validation fails
• route orbit read through the shared source decoder so non-ASCII Latin-1 characters are printed instead of replaced
• add regression tests for UTF-8 and ISO-8859-1 source content

Fixes #15.

Validation

• cargo fmt --all -- --check
• RUSTFLAGS="--deny warnings" cargo test (153 passed, 4 ignored)
• isolated CLI reproduction with ISO-8859-1 bytes B2 and E4: orbit read latin1 emitted UTF-8 C2 B2 (²) and C3 A4 (ä) with no replacement characters

[floze-the-genius]

CI reached the dependency audit after the build and failed on newly published RUSTSEC-2026-0204: crossbeam-epoch 0.9.18 is vulnerable and >=0.9.20 is patched. This PR does not change dependencies, and current trunk still locks 0.9.18, so the failure is baseline dependency drift rather than the source-encoding change. The remaining build matrix entries were then cancelled by fail-fast.

[chaseruskin]

Updated transitive dependencies on trunk. Please rebase off trunk and we will re-run the CI pipeline to verify all things check out.

[floze-the-genius]

Rebased onto current trunk in d9f91cf6. cargo fmt --all -- --check and cargo test --workspace --locked pass locally (153 passed, 4 ignored). Ready for the CI rerun.

[chaseruskin]

Thank you!