refactor: Move rust bindings to tket2._tket2

[aborgna-q]

First step towards #350.

Deinterlaces the rust-binded modules from the pure python ones. And puts them in _tket
For now, we still re-export everything directly, I'll add the python wrappers and missing typing info in a following PR.

[aborgna-q]

Removing the breaking change flag, since this only affects internal (_*) modules

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 85.33%. Comparing base (8aff57a) to head (e463cf5).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #351      +/-   ##
==========================================
+ Coverage   85.00%   85.33%   +0.32%     
==========================================
  Files          36       36              
  Lines        4554     4554              
  Branches     4293     4293              
==========================================
+ Hits         3871     3886      +15     
+ Misses        504      488      -16     
- Partials      179      180       +1     

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[ss2165]

nice