Add CMake uninstall target

[e345ee]

Summary

• Add a top-level cmake uninstall target for PhASAR.
• clean up empty PhASAR-owned install directories after uninstall.
• Document sudo ninja uninstall in the build instructions.

Fixes #556

Validation

• git submodule update --init --recursive
• pre-commit run --files BUILD.md CMakeLists.txt cmake/cmake_uninstall.cmake.in
• Docker-based full install/uninstall validation with LLVM 16 and clang-20:
  configure -> build -> install -> uninstall
• Verified that uninstall removes installed PhASAR files and empty PhASAR-owned install directories.

[Copilot]

Pull request overview

This PR adds a top-level CMake uninstall target to complement PhASAR’s existing install rules, and documents how to invoke it from Ninja builds.

Changes:

• Adds a top-level uninstall custom target that runs a generated CMake script.
• Introduces cmake_uninstall.cmake.in to remove files listed in install_manifest.txt and delete empty PhASAR-owned install directories.
• Documents sudo ninja uninstall in BUILD.md.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
CMakeLists.txt	Generates the uninstall script and registers a top-level uninstall target.
cmake/cmake_uninstall.cmake.in	Implements uninstall behavior (remove installed files + cleanup empty directories).
BUILD.md	Documents how to run the uninstall target from the build directory.

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[fabianbs96]

Hi @e345ee, thanks for contributing to PhASAR!

lgtm