Migrate from CMake FetchContent to CMake Package Manager (CPM)

[perhapsmaple]

This pull request migrates the project from using CMake FetchContent to CMake Package Manager (CPM).
Related Issue: Closes #286

Changes Made:

• Updated main CMakeLists.txt to fetch latest CPM.cmake script on execution
• Removed FetchContent-related commands from benchmark/CMakeLists.txt and test/CMakeLists.txt

Testing:

• I have tested the changes locally and ensured that the project builds successfully using CMake 3.24 on Ubuntu 22.04.
• I have verified that the correct versions of the packages are being fetched by CPM.

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[codecov]

Codecov Report

Merging #332 (583c09f) into master (0ae7045) will not change coverage.
The diff coverage is n/a.

❗ Current head 583c09f differs from pull request most recent head a43337e. Consider uploading reports for the commit a43337e to get more accurate results

@@           Coverage Diff           @@
##           master     #332   +/-   ##
=======================================
  Coverage   97.25%   97.25%           
=======================================
  Files          54       54           
  Lines        7934     7934           
=======================================
  Hits         7716     7716           
  Misses        218      218           

Flag	Coverage Δ
unittests	97.25% <ø> (ø)

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