[AhmetNSimsek]

This PR refactors retrieval decoders to support both file- and byte-based decoding.

Key changes:

• Introduces a Decoder abstraction with FILE and BYTES input modes.
• Allows decoders to define kwargs passed to the underlying reader.
• Preserves meaningful file suffixes in cache filenames.
• Moves path-capable formats such as NIfTI, GIFTI, FreeSurfer annotations, HDF5/NWB, NumPy, and tabular data to file-based decoding where appropriate. Gzip-compressed variants (e.g. .nii.gz, .csv.gz) are handled natively by their underlying readers when given a file path.
• Removes unnecessary file → bytes → file roundtrips and enables file-backed/lazy access where supported.
• Keeps find_suitable_decoder() as a backwards-compatible wrapper around Decoder.from_filename().
• Fixes ZipfileConnector to use ZipfileRequest directly instead of the bespoke ZipFileLoader, which was passing raw bytes to FILE-type decoders. ZipfileRequest correctly handles both decoder modes: BYTES decoders receive in-memory bytes, while FILE decoders have the zip member extracted to the siibra cache first and receive the path.
• Fixes RepositoryConnector.get_loader to pass the resolved Decoder directly to HttpRequest rather than wrapping it in a lambda, which also caused raw bytes to be passed to FILE-type decoders.
• Changes ZipfileRequest member matching from suffix-based to exact name matching, consistent with how ZipfileConnector.search_files returns full member paths.

Custom func= callbacks retain the existing byte-based behaviour.

[xgui3783]

If you have tested enough, then go for it.

My concern is commented.

[codecov]

Codecov Report

❌ Patch coverage is 79.56989% with 19 lines in your changes missing coverage. Please review.
✅ Project coverage is 46.21%. Comparing base (dd0f01f) to head (3036233).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
siibra/retrieval/requests.py	84.52%	13 Missing ⚠️
siibra/retrieval/repositories.py	0.00%	5 Missing ⚠️
siibra/configuration/factory.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #724      +/-   ##
==========================================
+ Coverage   45.94%   46.21%   +0.27%     
==========================================
  Files          74       74              
  Lines        8371     8393      +22     
==========================================
+ Hits         3846     3879      +33     
+ Misses       4525     4514      -11     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.