Keep inherited storage locations dynamic

[betacatsling]

Adding a child storage currently resolves the parent's other storage types and copies them into the child mapping. This freezes inherited cache/remote/data locations, so later parent changes and removals no longer reach the child.

Update only the explicitly stored entry at the target prefix when adding a storage. Regression coverage exercises all three add methods, parent replacement/removal, and preservation of the child override. All three cases fail on the unchanged base.

Validation on Linux/Python 3.12: 194 tests passed, 32 skipped; Ruff format/lint, project mypy and diff checks passed. No cloud storage was used. AI assistance was used for implementation and verification.

Prerequisite and revalidation: this branch now includes the shared CLI compatibility fix in #672 (4551489) followed by the original focused patch. This lets a fresh [tests,cli] installation run without external Click. The common change is separately reviewable and will disappear from this PR's diff once #672 is merged.

Revalidated the combined branch on Python 3.12 / Typer 0.27.2 with external Click absent: 200 passed / 32 skipped, mypy passed, and full source/test lint plus formatting passed with the repository-pinned Ruff 0.15.2. The benchmark workflow's base-branch step still needs #672 merged to main; it runs before the PR's code.

Fixes #665.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.23%. Comparing base (e38c8c2) to head (bebc836).
⚠️ Report is 72 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #666      +/-   ##
==========================================
+ Coverage   72.42%   74.23%   +1.80%     
==========================================
  Files          67       66       -1     
  Lines        5132     5418     +286     
  Branches      605      624      +19     
==========================================
+ Hits         3717     4022     +305     
+ Misses       1227     1203      -24     
- Partials      188      193       +5     

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