chore: Add default environments for Pixi tasks

[matthewfeickert]

Description

Follow up to PR #2638

• Pixi v0.63.0 added support for specifying a default environment for tasks. Using this, add a default environments task to remove the selection between the environment in which their feature exists and the 'dev' environment which includes the other environments.
  • c.f. https://github.com/prefix-dev/pixi/releases/tag/v0.63.0
• Add 'requires-pixi' of v0.63.0+ to ensure support for default environments.

Checklist Before Requesting Reviewer

• Tests are passing
• "WIP" removed from the title of the pull request
• Selected an Assignee for the PR to be responsible for the log summary

Before Merging

For the PR Assignees:

• Summarize commit messages into a comprehensive review of the PR

* Pixi v0.63.0 added support for specifying a default environment for tasks.
  Using this, add a default environments task to remove the selection between
  the environment in which their feature exists and the 'dev' environment which
  includes the other environments.
   - c.f. https://github.com/prefix-dev/pixi/releases/tag/v0.63.0
* Add 'requires-pixi' of v0.63.0+ to ensure support for default environments.

[matthewfeickert]

This feature was added in prefix-dev/pixi#5164 and released today (2026-01-14).

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.24%. Comparing base (42ef2cd) to head (a074666).
⚠️ Report is 29 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2661   +/-   ##
=======================================
  Coverage   98.24%   98.24%           
=======================================
  Files          65       65           
  Lines        4220     4220           
  Branches      464      464           
=======================================
  Hits         4146     4146           
  Misses         45       45           
  Partials       29       29           

Flag	Coverage Δ
contrib	98.12% <ø> (ø)
doctest	98.24% <ø> (ø)
unittests-3.10	96.44% <ø> (ø)
unittests-3.11	96.44% <ø> (ø)
unittests-3.12	96.44% <ø> (ø)
unittests-3.13	96.44% <ø> (ø)
unittests-3.9	96.49% <ø> (ø)

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