feat: separate deltin library and CLI packaging

[e54-bot]

Summary

• split the public deltin-rs library from the deltin-rs-cli executable package
• add public check, inspect, and compile facades while retaining explicit WIR interop
• preserve CLI UX and add package, CI, documentation, and regression coverage

Validation

• Rust 1.85 fmt, clippy, and workspace tests
• support matrix check
• library package dry-run and CLI workspace check

Fixes #80

[Teakowa]

Major — src/api.rs (compile_project/compile_path) and cli/src/main.rs (compile) implement and publish the compiler surface owned by #33, while #33 is still open and has not completed its end-to-end evidence/support-matrix gate. #80 explicitly says to coordinate with #33 and expose compile once that contract lands; this PR instead declares compile stable without any end-to-end-supported matrix evidence. Defer/remove the compile facade/CLI/docs from #80, or land the approved #33 compiler contract/evidence first and then make this PR consume it.

[Teakowa]

LGTM