Adopt package manager command classes

[edvilme]

Summary

Adopts the package manager command classes introduced in #1621 across Pip/UV, Conda, and Poetry.

Changes

• Replaces existing command construction and execution paths with the new command classes.
• Preserves existing command flags, environment targeting, version ordering, prerelease defaults, timeouts, and Poetry cwd behavior.
• Removes superseded utility wrappers and obsolete parser tests.
• Adds regression coverage for available-version precision, UV selection and tree targeting, and Conda upgrade semantics.

Dependency

This PR is stacked on #1621 and intentionally contains only the migration and cleanup commit. Review and merge #1621 first; this PR can then be retargeted to main.

Testing

• npm run lint
• npm run compile-tests
• npm run unittest (1,440 passing, 4 pending)

[edvilme]

Superseded by #1678. GitHub prevented retargeting this PR after registering it as part of the original stack; #1678 contains the same adoption commit and is correctly based on the smoke-test PR #1677.