Migrate the unified compiler to Catalyst

[mudit2812]

This PR migrates all source code for the unified compiler to Catalyst.

Changes:

• Add python_interface submodule to frontend/catalyst.
• Add python_interface submodule to frontend/test/pytest.
• Remove references to pennylane.compiler.python_compiler.
• Add a utils.py file to frontend/test/pytest to house data that is used by multiple test files.

Remaining work:

• Update the cookbook and associated notebooks to use catalyst.python_interface instead of pennylane.compiler.python_compiler.
• Migrate alll changelog pertaining to the unified compiler from PennyLane's changelog.

Questions for reviewers:

• Should I build wheels in this PR?
• Should xdsl and xdsl-jax be hard dependencies?

Future work:

• Add xDSL universe. This is needed to integrate lit testing for the unified compiler with the existing Catalyst infrastructure (see below).
• Integrate unified compiler testing with Catalyst's testing infrastructure. This will involve removing all unit/integration lit tests from the frontend/test/pytest folder and adapting them so that they can be moved to the frontend/test/lit folder.
• Begin the process of having documentation for the unified compiler on pennylane.ai.
• Improve test coverage for the unified compiler.
• Add tests and GitHub workflows to validate parity between xDSL and MLIR dialects.

[sc-99039] [sc-98172]

[paul0403]

Oh, the +20k lines 🤖

[mudit2812]

Oh, the +20k lines 🤖

I'm not really sure what the review procedure should be for this PR. Beyond linting and updates to which modules we're referencing (pennylane.compiler.python_compiler -> catalyst.python_interface), there aren't any changes.

[andrijapau]

Changes since last approval LGTM

[mehrdad2m]

for the lit failure on the check-catalyst workflow, we can add a # REQUIRES: xdsl to the top of the file and that I think should fix it

[dime10]

New test setup looks good to me 👍 The only thing I would like to sort out is the changelog (could also be a follow up if needed).

[mudit2812]

New test setup looks good to me 👍 The only thing I would like to sort out is the changelog (could also be a follow up if needed).

I'd prefer to address that later, as this PR is blocking quite a bit of work

[dime10]

Looks great 🎉