Add IR to Jet

[thisac]

Adds the IR to Jet, stored in python/ir. This folder contains the following:

• The grammar, parser and program class.
• A utilities file (used by parser/program)
• A usage guide (same as grammar.md in the IR repo) describing the syntax of the IR.
• The Strawberry Fields interface, consisting of a single file with a SF-to/from-IR-program converter function.
• A tests folder containing tests for the IR.

To-do/To-discuss

• Move tests to a better place (e.g., python/tests)
• Rewrite usage_guide.md to fit better with Jet.
• Add strawberryfields and lark to requirements.

[github-actions]

Test Report (C++) on Ubuntu

    1 files  ±0      1 suites  ±0   0s ⏱️ ±0s
239 tests ±0  239 ✔️ ±0  0 💤 ±0  0 ❌ ±0 
519 runs  ±0  519 ✔️ ±0  0 💤 ±0  0 ❌ ±0 

Results for commit c62d635. ± Comparison against base commit c62d635.

♻️ This comment has been updated with latest results.

[github-actions]

Test Report (C++) on MacOS

    1 files  ±0      1 suites  ±0   0s ⏱️ ±0s
239 tests ±0  239 ✔️ ±0  0 💤 ±0  0 ❌ ±0 
519 runs  ±0  519 ✔️ ±0  0 💤 ±0  0 ❌ ±0 

Results for commit c62d635. ± Comparison against base commit c62d635.

♻️ This comment has been updated with latest results.

[Mandrenkov]

Overall, looks good!

As a follow-up to our meeting, we should:

1. Update the formatter to comply with the standards set by SF and PL. Use make format to run the formatter locally.
2. Ensure the Python tests pass in the CI environment.
3. Add the required dependencies to requirements.txt (or requirement_test.txt).
4. (Future PR) Migrate the IR user guide to the "Using Jet" section of the documentation (docs/use).

[Mandrenkov]

Oh, and don't forget to update the changelog before you merge!

[Mandrenkov]

Thanks for the changes, Theo! I only ask that you address Josh's comment before merging.