Deprecate qml.from_qasm_file

[astralcai]

Context:
qml.from_qasm_file is an additional function to maintain that does not add much to the already existing qml.from_qasm. It is being deprecated, and users are directed to open the file themselves and load its content using qml.from_qasm.

Description of the Change:
Deprecation warning added to qml.from_qasm_file
Example code added to qml.from_qasm that reads a qasm file and loads with qml.from_qasm

Related Shortcut Issues:
[sc-56057]

[trbromley]

Thanks @astralcai!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.63%. Comparing base (e475db3) to head (224208b).
Report is 4 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5331      +/-   ##
==========================================
- Coverage   99.64%   99.63%   -0.01%     
==========================================
  Files         401      401              
  Lines       37294    36975     -319     
==========================================
- Hits        37160    36840     -320     
- Misses        134      135       +1     

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[trbromley]

Thanks @astralcai! Note that this led to another failure in the plugin tests: https://github.com/PennyLaneAI/plugin-test-matrix/actions/runs/8241505756/job/22538896791#step:8:626