As originally prompted by the fix recommended in conda/conda#12390 for the CI issue in #423 , this will use Mamba rather than Conda on the CIs, which not only has stable, accurate solves avoiding that issue and other potential similar ones, but also speeds up the Conda=yes jobs (which are currently the slowest) by around ≈2x total, and should also avoid the timeout/hang issues we sometimes see especially on macOS (and occasionally Windows).

Also:

• Create the environment for each binding and install packages all in one pass, rather than a separate install step for Qt/bindings, for a further substantial speedup
• Use a unique environment name for each binding to avoid needing to remove the environment before creating it
• Tweak various shell options for CI bash commands/scripts

Fixes #423