fix: add Cargo.lock to project template to avoid broken dependencies

[m4tx]

By pinning new project's dependencies to specific versions, we avoid problems like #187 which are caused by changes in the dependencies (in this case we were using a prerelease version of a dependency which updated one of its dependencies to edition=2024, but this will also prevent accidental semver-breaking changes from breaking our builds, too).

This also adds a justfile that makes it easy to update the lockfile.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 5 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
cot-cli/src/main.rs	0.00%	5 Missing ⚠️

Flag	Coverage Δ
rust	78.54% <0.00%> (-0.02%)	⬇️

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Files with missing lines	Coverage Δ
cot-cli/src/new_project.rs	95.12% <ø> (ø)
cot-cli/src/main.rs	0.00% <0.00%> (ø)