Fixing bugs/annoying issues and adding functionalities to lab_dev

[SamFerracin]

Description of the Change:

• Fixes the probability method for states, so that we can now normalize states with batched representations (i.e., in a superposition).
• Adds cutoffs argument to fock_state in fock.py, so that the Number state can now be initialized with a cutoff.
• Adds dm method to Ket, to compute the DM that corresponds to the given ket
• Uses astensor in the init of PolyExpAnsatz, so that Bargmann's A, b, and c can be given as lists and not necessarily as np.arrays.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 86.61%. Comparing base (e06c0c1) to head (d56167f).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #366 +/- ## =========================================== + Coverage 86.50% 86.61% +0.10% =========================================== Files 78 78 Lines 5661 5677 +16 =========================================== + Hits 4897 4917 +20 + Misses 764 760 -4 ``` | [Files](https://app.codecov.io/gh/XanaduAI/MrMustard/pull/366?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/states/base.py](https://app.codecov.io/gh/XanaduAI/MrMustard/pull/366?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=XanaduAI#diff-bXJtdXN0YXJkL2xhYl9kZXYvc3RhdGVzL2Jhc2UucHk=) | `96.61% <100.00%> (-0.15%)` | :arrow_down: | | [mrmustard/lab\_dev/states/states.py](https://app.codecov.io/gh/XanaduAI/MrMustard/pull/366?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=XanaduAI#diff-bXJtdXN0YXJkL2xhYl9kZXYvc3RhdGVzL3N0YXRlcy5weQ==) | `100.00% <100.00%> (ø)` | | | [mrmustard/physics/ansatze.py](https://app.codecov.io/gh/XanaduAI/MrMustard/pull/366?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=XanaduAI#diff-bXJtdXN0YXJkL3BoeXNpY3MvYW5zYXR6ZS5weQ==) | `94.85% <100.00%> (+0.08%)` | :arrow_up: | | [mrmustard/physics/converters.py](https://app.codecov.io/gh/XanaduAI/MrMustard/pull/366?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=XanaduAI#diff-bXJtdXN0YXJkL3BoeXNpY3MvY29udmVydGVycy5weQ==) | `100.00% <ø> (ø)` | | | [mrmustard/physics/fock.py](https://app.codecov.io/gh/XanaduAI/MrMustard/pull/366?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=XanaduAI#diff-bXJtdXN0YXJkL3BoeXNpY3MvZm9jay5weQ==) | `92.23% <100.00%> (+0.28%)` | :arrow_up: | | [mrmustard/physics/representations.py](https://app.codecov.io/gh/XanaduAI/MrMustard/pull/366?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=XanaduAI#diff-bXJtdXN0YXJkL3BoeXNpY3MvcmVwcmVzZW50YXRpb25zLnB5) | `99.40% <100.00%> (+<0.01%)` | :arrow_up: | ... and [2 files with indirect coverage changes](https://app.codecov.io/gh/XanaduAI/MrMustard/pull/366/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=XanaduAI) ------ [Continue to review full report in Codecov by Sentry](https://app.codecov.io/gh/XanaduAI/MrMustard/pull/366?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/366?dropdown=coverage&src=pr&el=footer&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=XanaduAI). Last update [e06c0c1...d56167f](https://app.codecov.io/gh/XanaduAI/MrMustard/pull/366?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).