[Transform #2] Transforms program

[rmoyard]

Description of the Change:

This PR introduces the main object of the transform rework, the Transform Program. We introduce it as a class with mulitple methods to interact with it.

Benefits:

We can store Transform programs on the QNode.

[rmoyard]

[sc-36419]

[github-actions]

Hello. You may have forgotten to update the changelog!
Please edit doc/releases/changelog-dev.md with:

• A one-to-two sentence description of the change. You may include a small working example for new features.
• A link back to this PR.
• Your name (or GitHub username) in the contributors section.

[codecov]

Codecov Report

Merging #4187 (24c92b0) into master (4777454) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff            @@
##           master    #4187    +/-   ##
========================================
  Coverage   99.77%   99.77%            
========================================
  Files         347      352     +5     
  Lines       31452    31649   +197     
========================================
+ Hits        31381    31578   +197     
  Misses         71       71            

Impacted Files	Coverage Δ
pennylane/fermi/fermionic.py	100.00% <ø> (ø)
pennylane/fermi/__init__.py	100.00% <100.00%> (ø)
pennylane/fermi/conversion.py	100.00% <100.00%> (ø)
pennylane/qnode.py	100.00% <100.00%> (ø)
pennylane/transforms/__init__.py	100.00% <100.00%> (ø)
pennylane/transforms/core/__init__.py	100.00% <100.00%> (ø)
pennylane/transforms/core/transform.py	100.00% <100.00%> (ø)
pennylane/transforms/core/transform_dispatcher.py	100.00% <100.00%> (ø)
pennylane/transforms/core/transform_program.py	100.00% <100.00%> (ø)

[mudit2812]

Thanks for the changes Romain! I just have one question and after that I'm ready to approve.

[mudit2812]

Thanks Romain! There's a test coverage issue, but that will need to be fixed before merging anyway so I'm happy to approve.

[BorjaRequena]

Thanks for the great work, @rmoyard!