[alexis900]

Closes #38 (IMP-15).

Summary

First CI for the neodev crate itself. Three jobs on ubuntu-latest, stable Rust, Swatinem/rust-cache:

Job	Command
Test	cargo test --locked
Clippy	cargo clippy --all-targets --locked -- -D warnings
Build (release)	cargo build --release --locked

Triggers: PRs to main, pushes to main. permissions: contents: read and a cancel-in-progress concurrency group.

Verified locally

cargo build --locked                              OK       0 warnings
cargo test --locked                               33 passed, 0 failed, 1 ignored
cargo clippy --all-targets --locked -- -D warnings  OK
cargo build --release --locked                    OK

The 5 clippy warnings that would have broken the new gate are fixed:

• unused std::time::UNIX_EPOCH import (vmm/vbox.rs)
• manual div_ceil → len().div_ceil(REGIONS_PER_NODE) (image.rs)
• needless borrow → std::fs::read_dir(root) (image.rs)
• needless range loop → nodes.iter().take(chunks.len()) (image.rs test)
• complex tuple type → FreeRegion / FreelistPlan type aliases (image.rs)

Not gated yet

• cargo fmt --check: cargo fmt --all -- --check currently reports 262 diff hunks across main. Formatting the whole crate is a separate, mechanical PR; gating it now would make this one red on arrival.
• Release publishing: prebuilt binaries are [ci] Publish prebuilt neodev binaries so downstream CI does not compile it #37.

Notes

• CONTRIBUTING.md says to branch and open PRs against develop, but the repository's branch is main. Left untouched here (docs drift); happy to fix it separately.
• No workflow existed before this PR, so this run is also the first execution of the new CI.