* Studio: fetch the release source asset for exact (mix) source builds
The source-build fallback rebuilt the codeload/archive URL from the
source repo and commit. A mix build's merged tree is never pushed to any
repo (it ships only as the release's llama.cpp-source-commit-<sha>.tar.gz
asset), so codeload 404s on the merge commit and an uncovered host could
not build from source. When an exact-source asset exists, fetch it
directly from the release and keep codeload as the fallback for vanilla
builds whose commit is real.
* [pre-commit.ci] auto fixes from pre-commit.com hooks
for more information, see https://pre-commit.ci
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Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>