Add control_flow module for for_loop and while_loop

[albi3ro]

Context:

for_loop and while_loop are currently located in qjit_api.py. This isn't an obvious location for these functions now that they have wider use and are "core" pennylane features.

Description of the Change:

Adds a control_flow module and places for_loop and while_loop into it.

Benefits:

Easier to find control flow code.

Possible Drawbacks:

Should consider moving qml.cond too, but it depends on Operator, queuing, MeasurementValue, etc.

Related GitHub Issues:

[sc-85453]

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.60%. Comparing base (2c3a11f) to head (c712562).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #7017   +/-   ##
=======================================
  Coverage   99.60%   99.60%           
=======================================
  Files         484      487    +3     
  Lines       46249    46257    +8     
=======================================
+ Hits        46065    46073    +8     
  Misses        184      184           

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