Gradle maven fallback streaming optymization

[matikepa]

Follow-up to #114

The performance fix so fallback metadata requests stream when metadata caching is off, which removes the buffering bottleneck in that path.

[andrew]

This branch currently has no diff against #114 (git diff between the two heads is empty), so the streaming change mentioned in the description doesn't seem to be pushed yet.

On the change itself: I flagged the buffering divergence in #114 as a behavioural note rather than a performance problem. The marker fallback path only handles plugin marker POMs (<1KB), checksum sidecars (~40 bytes) and maven-metadata.xml (a few KB). The streaming bypass in ProxyCached exists for things like npm packuments that can be megabytes; for these files buffering is fine. I don't think it's worth the extra code, so feel free to close this.

If you do still want to pursue it, please either retarget the base branch to gradle-plugin-fallback-support or wait until #114 merges and rebase, so the diff shows only the streaming change rather than all of #114.