Skip unchanged file section updates

[codeforester]

Summary

• Detect unchanged managed sections before update_file_section rewrites the target file.
• Demote unchanged and absent-remove paths to DEBUG logs while keeping INFO output for actual mutations.
• Cover unchanged section inode preservation and idempotent basectl update-profile output.

Validation

• bats lib/bash/file/tests/lib_file.bats
• bats cli/bash/commands/basectl/tests/update-profile.bats
• bash -n lib/bash/file/lib_file.sh
• env -u BASE_HOME HOME=/private/tmp/base-review-home BASE_TEST_PYTHON=/Users/rameshhp/.base.d/base/.venv/bin/python bin/base-test
• git diff --check

Closes #331