test: add regression test for --pull path nesting bug (#11005)

[hiba-q]

What changed and why?

This PR adds a failing regression test to tests/func/test_import.py to capture a path-resolution bug reported in Issue #11005.

Currently, running dvc exp run --pull on a repository where data was imported using dvc import --no-download behaves correctly the first time. However, if the local target directory is deleted, a subsequent --pull command improperly nests the source directory inside the target (creating target/source/... instead of target/...). This changes the directory structure and MD5 hash, breaking reproducibility.

How it was implemented:

I added a test using pytest and DVC's erepo_dir fixture that programmatically reproduces the exact workflow:

1. Initializes a repo and runs dvc import --no-download.
2. Runs dvc exp run --pull.
3. Deletes the target directory.
4. Runs dvc exp run --pull again.
5. Asserts that the improperly nested data/ directory does not exist.

Note: I am submitting this failing test first to provide a reproducible baseline while I continue investigating the ImportStage path mapping logic for a full fix.

References #11005

• ❗ I have followed the Contributing to DVC checklist.

• 📖 If this PR requires documentation updates, I have created a separate PR (or issue, at least) in dvc.org and linked it here.

Thank you for the contribution - we'll try to review it as soon as possible. 🙏

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[codecov]

Codecov Report

❌ Patch coverage is 5.88235% with 16 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.58%. Comparing base (2431ec6) to head (24c3ea2).
⚠️ Report is 201 commits behind head on main.

Files with missing lines	Patch %	Lines
tests/func/test_import.py	5.88%	16 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #11025      +/-   ##
==========================================
- Coverage   90.68%   88.58%   -2.11%     
==========================================
  Files         504      503       -1     
  Lines       39795    41014    +1219     
  Branches     3141     3243     +102     
==========================================
+ Hits        36087    36331     +244     
- Misses       3042     3999     +957     
- Partials      666      684      +18     

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