fix: unbreak cargo publish and stop shipping testdata in the crate

[tamada]

Summary

Fixes the cargo publish failure in the release pipeline, and stops the crate
from shipping test fixtures.

Both problems are live on main right now: run
30353306124
failed at publish_to_crates_io with

error: 1 files in the working directory contain changes that were not yet committed into git:
Cargo.lock

The Cargo.lock failure

main had Cargo.toml at 0.0.3 while the committed Cargo.lock still
recorded fauxrest 0.0.4. cargo publish re-resolves dependencies, rewrites
the lock file to match Cargo.toml, and then refuses to continue because the
working directory became dirty.

The drift comes from .github/scripts/update_version.sh, which rewrites
Cargo.toml and README.md but never touches Cargo.lock. Running
cargo build right after it regenerates the lock, and the existing
git commit -a in the same step picks it up — so this stops recurring.

The packaging change

Cargo.toml had no include/exclude, so cargo publish packaged the entire
repository. Adding exclude keeps testdata/, docs/, .github/ and
.vscode/ out of the published crate.

Order matters. Fixing Cargo.lock alone would make the next publish
succeed and upload testdata/ to crates.io. Both changes need to land
together, which is why they are in one pull request.

Also included

Six .vscode/tasks.json entries invoked the binary against a testdata
directory that no longer exists. They are removed; the remaining tasks are
untouched.

Verification

• cargo build and cargo test pass (66 tests + 13 doctests)
• Cargo.toml and Cargo.lock both report 0.0.3 after this change
• Merging this does not trigger publish.yaml — that workflow only runs for
  head branches matching releases/v*

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