Improved convert_to_bytes():
* Supports T (terabytes), P (petabytes), E (exabytes).
* Case-insensitive units (k or K, m or M, etc.)
* Returns raw integer bytes without B suffix.
* Falls back to raw bytes if no unit provided.
* Handles negative numbers gracefully.
Added convert_to_human_readable():
Both functions use 'echo' to display output and return 0 if
a conversion was possible. If a conversion was not possible,
display no output and give an exit code of 1.
Added SizeConversion test group to /p4/sdp/test/bsw/cli_tests.cfg
to test these function in the backup_function.sh library.