[cov] Enable coverage for ROM_EXT immutable section

[sasdf]

This PR enhances our coverage framework by integrating the ROM_EXT immutable section. It enables the collection of coverage data for this section from end-to-end tests run in rom_ext exec_env.

The changes include supporting runfiles propagation and adding essential coverage API calls to the immutable section's code.

The native cc_import rule lacks runfile propagation. Therefore, we've reimplemented _cc_import using objcopy and ar to address this.

Tested with:

$ ./bazelisk.sh coverage --config=ot_coverage \
  //sw/device/tests:uart_smoketest_fpga_cw340_rom_ext

$ genhtml -o /tmp/$USER/coverage --ignore-errors inconsistent,unsupported \
  bazel-out/_coverage/_coverage_report.dat \
| grep imm_section -A 1

Processing file sw/device/silicon_creator/rom_ext/imm_section/imm_section.c
  lines=26 hit=26 functions=2 hit=2
--
Processing file sw/device/silicon_creator/rom_ext/imm_section/imm_section_epmp.c
  lines=32 hit=28 functions=2 hit=2