Add Pixi to the repo

[IamPhytan]

Added Pixi to build the repo examples.

You can use Pixi with the following commands:

pixi run build-examples
# Run any example (ex: example-01)
pixi run example-01

blast-py is also available as a Python library when running pixi shell

$ pixi run python
>>> import blast
>>> blast.ManipulatorLimits()
<blast._blast_core.ManipulatorLimits object at 0x788a44f3f130>

[gallantandre]

Did you have trouble building or running? If so, please open an issue with specific platform details.

[gallantandre]

Thanks for the contribution. A few concerns before we merge this:

• Linux only. The pixi.lock file only covers linux-64, but the project already supports Windows and macOS as first-class targets (including the Python bindings). This adds no value for Windows users and would give new contributors a false impression that Pixi is the intended way to build on all platforms.
• Redundant with the existing setup. The repo already works out of the box with cmake -B build && cmake --build build. Dependencies are either vendored in extern/ or fetched via FetchContent. Adding a second parallel environment manager increases maintenance surface without a clear gain.
• Noisy lockfile. pixi.lock is 700+ lines and will produce large diffs on every dependency update.