Implement new polyexp ansatz

[kaspernielsen96]

Context: Updating MM to use the new polyexp ansatz Description of the Change: Renaming the new ansatz to PolyExpAnsatz and the old one to PolyExpAnsatzOld. Update mat_mul(and sub functions), fock,to_fock, to work with polynomials

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 95.45455% with 2 lines in your changes missing coverage. Please review.

Project coverage is 88.96%. Comparing base (3a6a35b) to head (48f633b).

Files	Patch %	Lines
mrmustard/physics/ansatze.py	91.66%	1 Missing :warning:
mrmustard/physics/gaussian_integrals.py	96.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #449 +/- ## =========================================== + Coverage 88.93% 88.96% +0.02% =========================================== Files 101 101 Lines 7076 7049 -27 =========================================== - Hits 6293 6271 -22 + Misses 783 778 -5 ``` | [Files](https://app.codecov.io/gh/XanaduAI/MrMustard/pull/449?dropdown=coverage&src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=XanaduAI) | Coverage Δ | | |---|---|---| | [mrmustard/lab\_dev/circuit\_components.py](https://app.codecov.io/gh/XanaduAI/MrMustard/pull/449?src=pr&el=tree&filepath=mrmustard%2Flab_dev%2Fcircuit_components.py&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=XanaduAI#diff-bXJtdXN0YXJkL2xhYl9kZXYvY2lyY3VpdF9jb21wb25lbnRzLnB5) | `97.71% <100.00%> (+0.03%)` | :arrow_up: | | [mrmustard/physics/representations.py](https://app.codecov.io/gh/XanaduAI/MrMustard/pull/449?src=pr&el=tree&filepath=mrmustard%2Fphysics%2Frepresentations.py&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=XanaduAI#diff-bXJtdXN0YXJkL3BoeXNpY3MvcmVwcmVzZW50YXRpb25zLnB5) | `99.51% <100.00%> (-0.01%)` | :arrow_down: | | [mrmustard/physics/ansatze.py](https://app.codecov.io/gh/XanaduAI/MrMustard/pull/449?src=pr&el=tree&filepath=mrmustard%2Fphysics%2Fansatze.py&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=XanaduAI#diff-bXJtdXN0YXJkL3BoeXNpY3MvYW5zYXR6ZS5weQ==) | `96.88% <91.66%> (+0.92%)` | :arrow_up: | | [mrmustard/physics/gaussian\_integrals.py](https://app.codecov.io/gh/XanaduAI/MrMustard/pull/449?src=pr&el=tree&filepath=mrmustard%2Fphysics%2Fgaussian_integrals.py&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=XanaduAI#diff-bXJtdXN0YXJkL3BoeXNpY3MvZ2F1c3NpYW5faW50ZWdyYWxzLnB5) | `98.06% <96.00%> (-0.43%)` | :arrow_down: | ------ [Continue to review full report in Codecov by Sentry](https://app.codecov.io/gh/XanaduAI/MrMustard/pull/449?dropdown=coverage&src=pr&el=continue&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=XanaduAI). > **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=XanaduAI) > `Δ = absolute (impact)`, `ø = not affected`, `? = missing data` > Powered by [Codecov](https://app.codecov.io/gh/XanaduAI/MrMustard/pull/449?dropdown=coverage&src=pr&el=footer&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=XanaduAI). Last update [3a6a35b...48f633b](https://app.codecov.io/gh/XanaduAI/MrMustard/pull/449?dropdown=coverage&src=pr&el=lastupdated&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=XanaduAI). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=XanaduAI).