fix: Replace rsync -az with -rlptDz to avoid permission issues

[Copilot]

The rsync function was using the -a (archive) flag which includes -o (preserve owner) and -g (preserve group) options that require superuser privileges to change file ownership. This caused "Operation not permitted" errors when downloading files from remote systems to local environments where users lack such privileges.

Problem:

rsync: chown "/path/to/file.tar.gz.temp" failed: Operation not permitted (1)
rsync error: some files/attrs were not transferred (see previous errors) (code 23)

Root Cause:
The -a flag is equivalent to -rlptgoD, where -o (preserve owner) and -g (preserve group) cause permission issues on systems where users cannot change file ownership.

Solution:
Replace -az with -rlptDz to maintain all useful archive functionality while excluding the problematic owner and group preservation options:

• -r: recursive
• -l: copy symlinks as symlinks
• -p: preserve permissions
• -t: preserve modification times
• -D: preserve device files and special files
• -z: compress during transfer

Changes:

• Modified dpdispatcher/utils/utils.py to use -rlptDz flags instead of -az
• Added comprehensive test coverage in tests/test_rsync_flags.py
• Updated comments to explain the permission issue fix

Testing:

• All existing tests pass with no regression
• New unit tests verify correct flag usage
• CLI functionality confirmed working
• Local rsync operations tested successfully

Fixes #434.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 47.60%. Comparing base (9d0f1a5) to head (6645340).
⚠️ Report is 1 commits behind head on master.

❗ There is a different number of reports uploaded between BASE (9d0f1a5) and HEAD (6645340). Click for more details.

HEAD has 1 upload less than BASE

Flag	BASE (9d0f1a5)	HEAD (6645340)
	15	14

Additional details and impacted files

@@             Coverage Diff             @@
##           master     #547       +/-   ##
===========================================
- Coverage   60.12%   47.60%   -12.53%     
===========================================
  Files          39       39               
  Lines        3905     3905               
===========================================
- Hits         2348     1859      -489     
- Misses       1557     2046      +489     

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