chore(cmake): replace deprecated FetchContent_Populate() calls

[SizzleUnrlsd]

Summary

Recent CMake versions emit deprecation warnings because the project still uses FetchContent_Populate() directly instead of FetchContent_MakeAvailable().

Affected files

• cmake/FetchNlohmannJson.cmake
• cmake/stackUsageAnalyzer.cmake
• cmake/httpLib.cmake

Why this should be fixed

Although configuration still succeeds, the current pattern is deprecated and may be removed in a future CMake release. This creates avoidable warnings and keeps the build system on a legacy FetchContent flow.

Proposed fix

Replace patterns like:

FetchContent_GetProperties(dep)
if(NOT dep_POPULATED)
    FetchContent_Populate(dep)
    add_subdirectory(${dep_SOURCE_DIR} ${dep_BINARY_DIR} EXCLUDE_FROM_ALL)
endif()