Support legacy tool receipts with PEP 508 requirements

[charliermarsh]

Summary

In #5494, I made breaking changes to the tool receipt format. This would break existing tools for all users. This PR makes the change backwards-compatible by supporting deserialization for the deprecated format.

Closes #5680.

Test Plan

Beyond the automated tests, you can run cargo run tool list on your existing machine.

Before:

warning: `uv tool list` is experimental and may change without warning
warning: Ignoring malformed tool `black` (run `uv tool uninstall black` to remove)
warning: Ignoring malformed tool `poetry` (run `uv tool uninstall poetry` to remove)
warning: Ignoring malformed tool `ruff` (run `uv tool uninstall ruff` to remove)

After:

warning: `uv tool list` is experimental and may change without warning
black v0.1.0
- black
poetry v1.8.3
- poetry
ruff v0.0.60
- ruff