clang-tidy: resolve performance-no-automatic-move

[greenc-FNAL]

No description provided.

[Copilot]

Pull request overview

This PR resolves a clang-tidy performance-no-automatic-move finding by adjusting index_router::route’s parameter to no longer be const when passed by value, enabling implicit move on return. It also updates the running clang-tidy fixes tracker documentation to mark the check as addressed.

Changes:

• Update index_router::route to take data_cell_index_ptr by value without top-level const, allowing an efficient implicit move in return index;.
• Mark performance-no-automatic-move as completed in the April 2026 clang-tidy fixes tracker and link the fixing PR.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
phlex/core/index_router.cpp	Removes top-level const from a by-value parameter to enable implicit move on return and satisfy clang-tidy.
docs/dev/clang-tidy-fixes-2026-04.md	Updates the checklist to reflect the check is fixed and references the PR that fixed it.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

@@            Coverage Diff             @@
##             main     #588      +/-   ##
==========================================
+ Coverage   82.62%   82.64%   +0.01%     
==========================================
  Files         161      161              
  Lines        5895     5895              
  Branches      682      682              
==========================================
+ Hits         4871     4872       +1     
  Misses        803      803              
+ Partials      221      220       -1     

Flag	Coverage Δ
scripts	76.12% <ø> (ø)
unittests	86.01% <ø> (+0.02%)	⬆️

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Files with missing lines	Coverage Δ
phlex/core/index_router.cpp	92.13% <ø> (ø)

... and 2 files with indirect coverage changes

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