Fixes # .

Summary/Motivation:

This should resolve ongoing issues with managing conda environments on Windows. conda install can get stuck (indefinitely) resolving the environment when installing scip on Windows/Python3.12. However, we cannot just kill conda at will: if conda has started installation, we must wait for it to complete. Instead of making the timeout longer (as in #3507), we will monitor the conda install process and only kill conda if it hasn't gotten to the installation phase when the timeout happens.

This PR supersedes #3507

Update: As part of getting this PR building, some additional development was required.

• we no longer need to explicitly install/activate the mamba solver (this is active by default in current conda environments)
• this PR enforces strict channel prioritization, which resolves several "indefinite hangs" we have been seeing when attempting to install packages on Python 3.12 and 3.13. Technically, it probably removes the need for the conda timeout logic entirely, however, that seems like a reasonable bit of "future proofing" to leave in.

Changes proposed in this PR:

• explicitly look up the conda install PID (and signal it directly)
• only signal conda if it hasn't started the installation process when the timeout happens.
• do not explicitly install the mamba solver in sufficiently new conda environments
• enforce strict channel prioritization

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