Solver meta issue

[wolfv]

There are a couple of solver related issues:

Fixed by inspecting variants & variant deps

• mamba brings pypy instead of CPython when creating env #658
• Add a test with equal variants and make sure that mamba solves it fine #91
• Mamba resolves to older packages than Conda #848
• Wrong build of mpich selected with metapackage #924

Channel priority issues

• Properly set channel priorities: Channel priority not maximized over competing goals #532
• Properly do "strict" prio: mamba resolves an environment while conda throws a conflict #559
• Solver sometimes stuck in a loop: Mamba solver sometimes stuck in a loop (when combining defaults + conda-forge) #1044
• Solver is hanging solver is hanging #577

Other solver related issues

• Force flag for remove: mamba remove package doesn't respect --force flag #412
• Freeze installed solver option: Implement the FREEZE_INSTALLED solver option #404
• Mamba install -c local mamba install -c local #434
• Respect channel pin with update Respect channel specs with mamba update #911
• Update all not getting highest build number: update --all may not get highest build number #747
• Update all dependencies: properly update all dependencies during update #52
• Prune with mamba install / mamba env install Support --prune flag in 'mamba install'  #688
• Complex update doesn't update package Complex update (pyarrow nightly from custom channel) gives "nothing to do" #837
• Solver timeout timeout on solver #580