Minor conda script changes

[bwohlberg]

• svmbir is now available via conda
• install mamba as faster alternative to conda management interface
• delete attempt to install now-defunct _license package

[codecov]

Codecov Report

Merging #222 (9f9950b) into main (c084dda) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #222   +/-   ##
=======================================
  Coverage   92.42%   92.42%           
=======================================
  Files          49       49           
  Lines        3431     3431           
=======================================
  Hits         3171     3171           
  Misses        260      260           

Flag	Coverage Δ
unittests	92.42% <ø> (ø)

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