chore: stop ignoring and start tracking Cargo.lock

Cargo.lock should be tracked for binaries according to best practices.

.gitignore

@@ -10,10 +10,6 @@ src/days_mod.inc
 debug/
 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