Fix duplicate local dependencies in pip install command

[basnijholt]

Summary

• Fixed a bug where local dependencies referenced by multiple projects were duplicated in the pip install command
• Added comprehensive test coverage for the deduplication logic
• The issue was causing packages to appear multiple times (e.g., 9 times) in CI builds

Problem

When multiple projects reference the same local dependency through local_dependencies: in their requirements.yaml, the dependency was being added multiple times to the pip install command. This was observed in CI where third_party/cypress appeared 9 times in a single pip install command.

Root Cause

The deduplication logic in _install_command function was flawed:

• It created installable_set from existing packages
• But didn't update this set while iterating through local_dependencies.values()
• If the same dependency appeared in multiple projects' local_dependencies, it would be added multiple times

Solution

Updated the deduplication logic to maintain the installable_set as dependencies are added:

# Now properly updates the set to prevent duplicates
for deps in local_dependencies.values():
    for dep in deps:
        dep_resolved = dep.resolve()
        if dep_resolved not in installable_set:
            installable.append(dep)
            installable_set.add(dep_resolved)  # Key fix

Test Plan

• Added test test_no_duplicate_local_dependencies_in_install_command that reproduces the issue
• Test fails without the fix (showing 3 duplicates)
• Test passes with the fix (showing proper deduplication)
• Existing tests continue to pass

Related Issues

• Observed in CI: https://github.com/ionq/system_performance/actions/runs/17304244901/job/49123013838?pr=925

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📚 Documentation preview 📚: https://unidep--255.org.readthedocs.build/en/255/

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.13%. Comparing base (06be4a8) to head (09dfdc8).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #255   +/-   ##
=======================================
  Coverage   97.12%   97.13%           
=======================================
  Files          10       10           
  Lines        1497     1502    +5     
=======================================
+ Hits         1454     1459    +5     
  Misses         43       43           

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