Fix compressed media backup restoration

[Copilot]

Description

Restoring compressed media backups fails with tarfile.ReadError: invalid header when using the --uncompress flag. The issue occurs because mediarestore.py relies on tarfile's built-in gzip decompression (mode="r:gz"), which doesn't work reliably with all file-like objects after storage operations.

Changes:

• Modified mediarestore.py to use utils.uncompress_file() before opening tarfile, matching the pattern in dbrestore.py
• Added test coverage for compressed and uncompressed media backup restoration
• Updated changelog

The fix ensures decompression happens explicitly before tarfile processing:

# Before: Unreliable with file-like objects
tar_file = tarfile.open(fileobj=input_file, mode="r:gz" if self.uncompress else "r:")

# After: Explicit decompression first
if self.uncompress:
    uncompressed_file, input_filename = utils.uncompress_file(input_file, input_filename)
    input_file.close()
    input_file = uncompressed_file

tar_file = tarfile.open(fileobj=input_file, mode="r:")

Checklist

Please update this checklist as you complete each item:

• Tests have been developed for bug fixes or new functionality.
• The changelog has been updated, if necessary.
• Documentation has been updated, if necessary.
• GitHub Issues closed by this PR have been linked.

_{By submitting this pull request I agree that all contributions comply with this project's open source license(s).}

Original prompt

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This section details on the original issue you should resolve

<issue_title>restore compresses backup will not work</issue_title>
<issue_description>
Restore a compressed media backup results in:

  File "/home/jens/repos/PyInventory/.venv/lib/python3.12/site-packages/dbbackup/management/commands/mediarestore.py", line 67, in handle
    self._restore_backup()
  File "/home/jens/repos/PyInventory/.venv/lib/python3.12/site-packages/dbbackup/management/commands/mediarestore.py", line 104, in _restore_backup
    else tarfile.open(fileobj=input_file, mode="r:")
         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/tarfile.py", line 1875, in open
    return func(name, filemode, fileobj, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/tarfile.py", line 1907, in taropen
    return cls(name, mode, fileobj, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/tarfile.py", line 1765, in __init__
    self.firstmember = self.next()
                       ^^^^^^^^^^^
  File "/usr/lib/python3.12/tarfile.py", line 2753, in next
    raise ReadError(str(e)) from None
tarfile.ReadError: invalid header

I used django-dbbackup v5.0.1 for creating and restore of the backup.
btw.: it worked without compression ;)

</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes restore compresses backup will not work #647

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