specs can be requested at a specific stage of the transform program

[Shiro-Raven]

Context:
Currently, specs() can only be requested after applying the full transform program, with the exception of the stages provided through expansion_strategy.

Description of the Change:
Using the new level argument from construct_batch, the function is adapted to make use of the argument as well, which allows for more flexible requests and ability to pinpoint when exactly to ask for specs. In addition, the function works with transforms that split the tape, returning a list of dictionaries each corresponding to one of the new tapes.

Benefits:
More flexible resource estimation.

[sc-53736] Fixes #5706

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.67%. Comparing base (1bf7682) to head (4046c97).
Report is 247 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5781      +/-   ##
==========================================
- Coverage   99.68%   99.67%   -0.01%     
==========================================
  Files         421      421              
  Lines       40437    40139     -298     
==========================================
- Hits        40309    40009     -300     
- Misses        128      130       +2     

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[albi3ro]

🎉 Glad for this to finally be getting finished up!

[Jaybsoni]

Great work, I can't wait to play around with this feature myself! I left a few small changes to be addressed.

Additionally, I found a bug! When passing in level = "device", we lose the error key of the specs dictionary. This is because we compute the error on the decomposed tape, but the error is only defined for templates which get decomposed into fundamental gates. I can share an example of this with you offline and we can discuss how best to support it !

[Jaybsoni]

Great work!