feat: support script mode in setup.cfg

[noahp]

Add the entry needed to run as a console script. This enables usage models like so:

pip install elf-diff

# run the script standalone, without python -m
elf_diff ...

# use uvx to run the script in one shot
uvx elf_diff ...

For testing, uvx can be invoked like so locally:

uvx --no-cache --from . -- \
  elf-diff --html_dir report tests/x86_64/libelf_diff_test_debug_old.a tests/x86_64/libelf_diff_test_debug_new.a