add rust-toolchain and lock dependencies (#26)

# What ❔

This PR adds rust-toolchain file to set a specific toolchain version,
adds Cargo.lock to source control to lick the dependencies and adjusts
the CI script to use the specific version from rust-toolchain.

## Why ❔

Unspecified toolchain and unlocked dependencies are a source of
compilation issues.

## Checklist

- [x] PR title corresponds to the body of PR (we generate changelog
entries from PRs).

.github/workflows/build.yaml

@@ -49,15 +49,15 @@ jobs:
       - name: Setup rust
         run: |
           rustup set profile minimal
-          rustup toolchain install nightly-2023-04-17
-          rustup default nightly-2023-04-17
+          rustup toolchain install nightly-2023-06-25
+          rustup default nightly-2023-06-25
 
       - name: Build tests and copy binaries to a separate dir
         shell: bash
         run: |
           mkdir artifacts
           CUDAARCHS=80 CARGO_TARGET_DIR=./build \
-          cargo +nightly-2023-04-17 test --no-run --release --message-format=json -q \
+          cargo +nightly-2023-06-25 test --no-run --release --message-format=json -q \
           | jq -r 'select(.executable != null) | .executable' \
           | while read binary; do
             cp "$binary" artifacts/

.gitignore

@@ -2,10 +2,6 @@
 # will have compiled files and executables
 /target/
 
-# Remove Cargo.lock from gitignore if creating an executable, leave it for libraries
-# More information here https://doc.rust-lang.org/cargo/guide/cargo-toml-vs-cargo-lock.html
-Cargo.lock
-
 # These are backup files generated by rustfmt
 **/*.rs.bk