refactor(context): normalize in homedir instead

[hirehamir]

What Does This PR Try to Resolve?

This is a follow-up to #17204.

That fix normalized inside read_packages.

As noted in review, Cargo prefers to normalize at the exterior and assume interiors are clean.

This change moves the normalize_path to homedir, and removes the interior normalization.

How to Test and Review This PR?

• config_symlink_home_duplicate_load and install_git_with_symlink_home pass. Symlink handling appears undisturbed.
• no_duplicate_package_warning_with_dotdot_cargo_home (added in fix(source): incorrect duplicate package warning #17204) still passes. The exterior placement fixes the same issue.

cargo test --test testsuite -- no_duplicate_package_warning_with_dotdot_cargo_home config_symlink_home_duplicate_load install_git_with_symlink_home

[rustbot]

r? @weihanglo

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Why was this reviewer chosen?

The reviewer was selected based on:

• Owners of files modified in this PR: @epage, @weihanglo
• @epage, @weihanglo expanded to epage, weihanglo
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