Fix consumer macOS CI install path by using workspace-local prefix

[Copilot]

consumer macos-latest failed in CI because the consumer job installed trx-cpp into /usr/local, which is not writable on hosted macOS runners. This change redirects installation to a writable workspace prefix and aligns downstream package discovery with that location.

• Root cause

  • Consumer job used cmake --build ... --target install, which defaulted to /usr/local and failed on directory creation (/usr/local/lib).

• Workflow changes

  • Replaced build-target install invocation with explicit cmake --install and a local prefix under ${{ github.workspace }}.
  • Updated consumer configure step to use the same install root in CMAKE_PREFIX_PATH.

• Impact

  • Keeps the consumer validation semantics intact (find_package(trx-cpp CONFIG REQUIRED)), while removing macOS permission dependency on system install paths.

- name: Build and install trx-cpp
  run: cmake --install build --config Release --prefix "${{ github.workspace }}/build/install"

# ...
-DCMAKE_PREFIX_PATH="${GITHUB_WORKSPACE}/build/install"

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.66%. Comparing base (5cf07d1) to head (90f669a).

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #57   +/-   ##
=======================================
  Coverage   88.66%   88.66%           
=======================================
  Files          15       15           
  Lines        7765     7765           
  Branches     1044     1044           
=======================================
  Hits         6885     6885           
  Misses        880      880           

Flag	Coverage Δ
linux	87.86% <ø> (ø)
macos	88.50% <ø> (ø)

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