* phase2: remove unused git_ssh plumbing

 * scripts: remove unused expire.sh
 * phase2: remove unused tree_expire option and steps
 * phase2: rsync: use --size-only instead of --checksum for sourceupload
 * phase2: use sha2rsync.pl for 'targetupload'
 * phase2: compute checksums
 * phase2: reduce verbosity of rsync and use rsync.sh helper
 * phase2: don't enable rsync compression where unnecessary
 * phase2: regroup common rsync options and add timeout
 * phase2: report ccache stats at end of build
 * Revert "phase2: use full git history for reproducibility"
 * phase2: use Interpolate instead of WithProperties
 * phase2: s/SetProperty/SetPropertyFromCommand/
 * phase2: do not exceed nproc build concurrency
 * phase2: remove unused 'other_builds' property
 * phase1: treat all branches equally for building
 * phase1: raise priority of tag builds
 * ci: split container push steps to separate job and add deploy tag
 * ci: generalize container test step
 * ci: move git short sha length to ENV
 * docker,worker: install zstd
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