Fix Version/s: None
Tarball builds are so slow to solve that more than half of the 8 hour time limit is being used on conda. State is being kept, but newinstall intentionally reinstalls the environment even if it already exists. (DM-31235 attempted to reuse an existing environment, but it failed and had to be reverted.) As an immediate fix, using lsstinstall instead of newinstall should speed things up massively. Unfortunately, using lsstinstall on top of an existing newinstall installation has some problems.
A somewhat simpler solution is to modify newinstall to install mamba and then use that to create the environment. This doesn't provide some of the other features of lsstinstall, but it's 100% compatible and much faster.
Turns out that there are issues putting lsstinstall on top of an existing newinstall. Had to revert. Looking into a different fix.
This should get us unstuck for nightly and weekly builds. stack-os-matrix is harder to fix as that is lsstsw and not newinstall.