[Swatantra-66]

Summary

Addresses apache/nuttx#19549 by closing the CMake build-system parity gap in apps/audioutils

1. audioutils/morsey:
   Adds CMakeLists.txt using CMake FetchContent to download the upstream v1.0.1 release tarball.
   Implements automated SHA-256 integrity verification for morsey.c and morsey.h matching Makefile.
   Exports the public header via symlink to ${NUTTX_APPS_BINDIR}/include/audioutils/morsey.h.
   Compiles morsey.c and registers private include paths with the apps library target.

2. audioutils/rtttl-c:
   Adds CMakeLists.txt using CMake FetchContent to shallow clone tag v0.1.0.
   Implements automated SHA-256 integrity verification for rtttl.c and rtttl.h matching Makefile.
   Exports the public header via symlink to ${NUTTX_APPS_BINDIR}/include/audioutils/rtttl.h.
   Compiles rtttl.c and registers private include paths with the apps library target.

3. Robustness & Edge-Case Safety (both modules):
   Preapps Safety: Conditioned on if(CONFIG_* AND TARGET apps) to prevent premature evaluation during early Kconfig generation.
   Offline Build Overrides: Honors FETCHCONTENT_SOURCE_DIR_MORSEY_FETCH and FETCHCONTENT_SOURCE_DIR_RTTTL_C_FETCH without attempting network access.
   Local Edit Preservation: Rejects missing/incomplete checkouts with a fatal error if local files exist, refusing to delete developer modifications or Make checkouts.
   Subbuild Reset: Wipes sub-build state under ${FETCHCONTENT_BASE_DIR} to ensure recovery when a fresh download is needed.
   Symlink Refresh: Unconditionally invokes nuttx_create_symlink to refresh exported header links whenever the active source directory changes.

Impact

New feature added: Yes, CMake build support for audioutils/morsey and audioutils/rtttl-c.
Existing behavior changed: No, existing Make builds remain 100% untouched.
Build process: Enables building both modules when configuring with CMake (-DCONFIG_AUDIOUTILS_MORSEY=y and -DCONFIG_AUDIOUTILS_RTTTL_C=y).
Compatibility: Fully compliant with cmake-format (0 warnings/errors).

Testing

Host: Ubuntu 24.04 (WSL2 / Windows 11 x86_64), GCC 15.2.0, CMake 4.2.3, Ninja 1.13.2
Target: sim:nsh (-DCONFIG_AUDIOUTILS_MORSEY=y -DCONFIG_AUDIOUTILS_RTTTL_C=y)

Build Logs:

-- Populating morsey_fetch
[1/9] Performing download step (download, verify and extract) for 'morsey_fetch-populate'
-- extracting... done
[9/9] Completed 'morsey_fetch-populate'
-- Populating rtttl_c_fetch
[1/9] Performing download step (git clone) for 'rtttl_c_fetch-populate'
Cloning into 'rtttl-c'...
HEAD is now at a093e61 Release under Apache-2.0, too
[9/9] Completed 'rtttl_c_fetch-populate'
-- Build files have been written to: .../build_audiotest
ninja: Entering directory `build_audiotest'
[3/35] Building C object apps/CMakeFiles/apps.dir/audioutils/morsey/morsey/morsey.c.o
[8/35] Building C object apps/CMakeFiles/apps.dir/audioutils/rtttl-c/rtttl-c/rtttl.c.o
[35/35] Linking C static library apps/libapps.a

Style & Format Verification:

cmake-format --check apps/audioutils/morsey/CMakeLists.txt
cmake-format --check apps/audioutils/rtttl-c/CMakeLists.txt
100% CMAKE-FORMAT COMPLIANT

[Swatantra-66]

Removed the SHA checks and streamlined both CMakeLists.txt to follow the standard NuttX FetchContent pattern matching other submodules