[benchmark] use `mamba` in environment construction

[zacharyburnett]

the conda environment construction in asv currently fails on tangra3 due to the current setup; however, switching the environment_type to mamba does work.

mamba is a rewrite of conda that is both significantly faster in the environment resolution step and has parity of commands with conda. Since the regular benchmarking on tangra3 creates an environment, it makes sense to use mamba going forward.

asv currently supports environment_type = mamba in its main branch code, and AFAIK this will be included in the next release. For now, the tangra3 benchmarks use pip install git+https://github.com/airspeed-velocity/asv.git

Checklist

• [ ] ~added entry in CHANGES.rst (either in Bug Fixes or Changes to API)~
• [ ] ~updated relevant tests~
• [ ] ~updated relevant documentation~
• [ ] updated relevant milestone(s)
• [x] added relevant label(s)

[codecov[bot]]

Codecov Report

Patch and project coverage have no change.

Comparison is base (2256c48) 75.36% compared to head (6b4ebb8) 75.36%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #185 +/- ## ======================================= Coverage 75.36% 75.36% ======================================= Files 33 33 Lines 6039 6039 ======================================= Hits 4551 4551 Misses 1488 1488 ```

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[kmacdonald-stsci]

What is the advantage of Mamba over Conda? That's not explained in this PR.

[zacharyburnett]

What is the advantage of Mamba over Conda? That's not explained in this PR.

Whoops, sorry! updated the description

[nden]

Now that benchmarks are in bench, should this be closed?