Support build from source through cargo

[spywhere]

Addressed #28 😄

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Note

Adds cargo-based source install support (latest/version/commit), updates README with instructions, adjusts tests, and tweaks CI to remove cargo before tests.

• Install script (bin/install):
  • Add cargo-based source installation via ref:* (supports latest, semver, and full commit SHA) with install_from_source.
  • Retain archive-based installs for release versions via install_from_archive.
  • Validate cargo presence for source builds; error with clear message if missing.
• Docs (README.md):
  • Document source install flow and dependency on cargo (via asdf-rust).
  • Add examples for ref:<version>, ref:latest, and ref:<full-commit-hash>.
• Tests (test/install.bats):
  • Update failure expectation to require cargo when using ref.
• CI (.github/workflows/workflow.yml):
  • Add step to remove preinstalled cargo before tests.

^{Written by Cursor Bugbot for commit 9abe82e. This will update automatically on new commits. Configure here.}

[spywhere]

@smorimoto sorry for pinging directly but is there anything needed to have this merged?

[smorimoto]

I will check this tonight.

[spywhere]

I'll address comments, hopefully within today

[smorimoto]

bugbot run