feat: add pixi build options

[tsutterley]

ci: use pixi for build
docs: use pixi for build

[Copilot]

Pull Request Overview

This PR migrates the project's build and dependency management system from conda/mamba to pixi, providing a more streamlined workspace environment for development and documentation building.

• Replaces conda environment files with pixi configuration in pyproject.toml
• Updates CI/CD workflows to use pixi instead of mamba
• Adds comprehensive documentation for pixi usage and installation

Reviewed Changes

Copilot reviewed 10 out of 12 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
readthedocs.yml	Updates Read the Docs build configuration to use pixi instead of conda
pyproject.toml	Adds pixi workspace configuration, tasks, and feature dependencies
environment.yml	Removes conda environment file (replaced by pixi config)
doc/environment.yml	Removes documentation-specific conda environment file
doc/source/project/Testing.rst	Updates testing documentation to include pixi commands
doc/source/getting_started/Install.rst	Adds pixi installation and usage documentation
doc/source/conf.py	Adds ReadTheDocs detection and warning suppression
README.md	Adds pixi installation and usage instructions
MANIFEST.in	Updates file exclusions for new build system
.github/workflows/python-request.yml	Migrates CI workflow from mamba to pixi

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[Copilot]

The pixi installation commands should be prefixed with proper YAML command formatting. Each command should be a single string in the list.

Suggested change

	- asdf plugin add pixi
	- asdf install pixi latest
	- asdf global pixi latest
	install:
	- pixi install -e doc
	build:
	html:
	- pixi run -e doc sphinx-build -T -b html doc/source $READTHEDOCS_OUTPUT/html
	- "asdf plugin add pixi"
	- "asdf install pixi latest"
	- "asdf global pixi latest"
	install:
	- "pixi install -e doc"
	build:
	html:
	- "pixi run -e doc sphinx-build -T -b html doc/source $READTHEDOCS_OUTPUT/html"

[Copilot]

The 'html' key should be at the same indentation level as 'build' since it's the build format specification, not a nested job step.

Suggested change

	html:
	- pixi run -e doc sphinx-build -T -b html doc/source $READTHEDOCS_OUTPUT/html
	html:
	- pixi run -e doc sphinx-build -T -b html doc/source $READTHEDOCS_OUTPUT/html