Refactor object read streams to work via object sources

Hi,

the git_istream data structure can be used to read objects from the object database in a streaming fashion. This is used for example to read large files that one doesn't want to load into memory in full.

In the current architecture, all the logic to handle these streams is fully self-contained in "streaming.c". It contains the logic to set up streams for loose, packed, in-memory and filtered objects. This doesn't really play all that well with pluggable object databases, as it should be the responsibility of the object database source itself to handle the logic.

This patch series thus revamps our object read streams: instead of being entirely contained in "streaming.c", the format-specific streams are now created by the ODB sources. This allows each source itself to decide whether and, if so, how to make objects streamable.

This overall requires quite a bit of refactoring, but I think that the end result is an easier-to-understand infrastructure that is an improvement even without pluggable object databases.

This series is built on...

Thanks!

Patrick

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{ "series": { "revision": 1, "change-id": "20251107-b4-pks-odb-read-stream-7ea7f0e0a8f4", "prefixes": [] } }

Closes Move streaming of objects into backends (#610 - closed).