Update pixi.toml

[jorisv]

• Use python 3.10 as oldest python
• Use python 3.14 as latest python version
• Remove latest pixi warning
• Check if we can remove default variable initialization
  • We can't
• Remove some activation scripts
• Improve ccache statistics
• Improve language server integration
• Setup pixi build
• Use conda clang-cl on windows build

[ManifoldFR]

I rebased the branch. When trying to update the lockfile, I got the following error:

Error:   × failed to solve requirements of environment 'test-pixi-build' for platform 'linux-64'
  ├─▶   × failed to extract metadata for package 'eigenpy'
  │
  ├─▶   × could not initialize the build-backend
  │
  ├─▶   × failed to parse configuration
  │
  ╰─▶   × unknown field `targets`, expected one of `extra-args`, `env`, `debug-dir`, `debug_dir`, `extra-input-globs`, `compilers`