Converter for MPS DMRG wavefunctions

[Chiffafox]

Context:

Continuing to expand the capabilities of the qml.qchem.import_state to allow more diverse wavefunction ansatze to be used to initialize quantum algorithms

Description of the Change:

The function can now import MPS DMRG wavefunctions generated by the Block2 code, in their Slater determinant reconstruction.

Benefits:

Possible Drawbacks:

Related GitHub Issues:

[soranjh]

[sc-43870]

[Jaybsoni]

Lots of small comments, might have to copy some changes from the other PR to make sure they match in the _sitevec_to_fock function

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (e909e56) 99.62% compared to head (d43a939) 99.62%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4523   +/-   ##
=======================================
  Coverage   99.62%   99.62%           
=======================================
  Files         375      375           
  Lines       33443    33472   +29     
=======================================
+ Hits        33318    33347   +29     
  Misses        125      125           

Files Changed	Coverage Δ
pennylane/qchem/convert.py	100.00% <100.00%> (ø)

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[Jaybsoni]

Looks good, I think the efficiency of some implementations could be improved but I doubt it would make a significant difference to performance now so happy to approve 👍🏼