Make relative_paths_like Optional and Allow Custom Decryption Chunk Size

[KnugiHK]

This PR makes two changes:

Make relative_paths_like Optional

Based on the validation logic in the extract_files function:

# Check the provided arguments and replace missing ones with wildcards:
if relative_paths_like is None and domain_like is None:
    # If someone _really_ wants to try and extract everything, then setting both to '%' should be enough.
    raise ValueError("At least one of 'relative_paths_like' or 'domain_like' must be specified!")
elif relative_paths_like is None and domain_like is not None:
    relative_paths_like = "%"
elif relative_paths_like is not None and domain_like is None:
    domain_like = "%"

The relative_paths_like parameter appears to be optional (at least it seems to me that). Thus, it should be set to None by default.

Allow Custom Decryption Chunk Size

I found the default chunk size (100MB) drives the decryption process very slow, especially when dealing with a lot of WhatsApp media files. Therefore, a parameter has been added to the EncryptedBackup class for adjusting the chunk size.

[KnugiHK]

For extract_files function, the default values of relative_paths_like and domain_like can acutally be set to "%". By doing so, no checking is needed. The following is the diff of the change:

-   def extract_files(self, *, relative_paths_like=None, domain_like=None, output_folder,
+   def extract_files(self, *, relative_paths_like="%", domain_like="%", output_folder,
                      preserve_folders=False, domain_subfolders=False, incremental=False,
                      filter_callback=None):
        """

@@ -333,14 +333,6 @@ class EncryptedBackup:
        # Ensure that we've initialised everything:
        if self._temp_manifest_db_conn is None:
            self._decrypt_manifest_db_file()
-       # Check the provided arguments and replace missing ones with wildcards:
-       if relative_paths_like is None and domain_like is None:
-           # If someone _really_ wants to try and extract everything, then setting both to '%' should be enough.
-           raise ValueError("At least one of 'relative_paths_like' or 'domain_like' must be specified!")
-       elif relative_paths_like is None and domain_like is not None:
-           relative_paths_like = "%"
-       elif relative_paths_like is not None and domain_like is None:
-           domain_like = "%"
        # If the filter function is not provided, default to including everything:
        _include_fn = filter_callback if callable(filter_callback) else (lambda **kwargs: True)
        # Use Manifest.db to find the on-disk filename(s) and file metadata, including the keys, for the file(s).

I can add this commit to the PR if you want.