Move code to ITensors.ITensorMPS

[emstoudenmire]

This PR moves all of the code in this package to the ITensors.ITensorMPS module.
Other changes:

• Reexport added as a dependency
• For now, ITensorTDVP.dmrg defined to call ITensorMPS.alternate_dmrg
• Some tests and example code updated to reflect new location of code

[emstoudenmire]

Tests are not passing yet, of course, because the companion PR (ITensor/ITensors.jl#1366) in ITensors.jl is not merged.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (738c5f5) to head (010a696).

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Additional details and impacted files

@@             Coverage Diff              @@
##             main       #67       +/-   ##
============================================
+ Coverage   85.87%   100.00%   +14.12%     
============================================
  Files          17         1       -16     
  Lines         524         1      -523     
============================================
- Hits          450         1      -449     
+ Misses         74         0       -74     

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[emstoudenmire]

The latest commits revert back to the previous style of wrapping functions moved to ITensors.ITensorMPS, which have itensortdvp_ at the beginning.