Fix batch execute single tape

[antalszava]

Changes

• Changes the batch_execute method to support executing single tapes as per
  PennyLane v0.20.0 where batch execution is the default for a QNode.

Also, fixes issues that came from updates in PennyLane and in the Z-Quantum libraries:

• Fixed an import to use from zquantum.core import circuits;
• Pulls the import_from_qiskit function from qeqiskit.conversions;
• Updates the logic to pass the n_samples to the methods being used from z-quantum-core rather than using it while creating a backend (create_object);
• Updates to using the new qml.matrix top-level function.

Also added Python 3.9 and Python 3.10 runners.

[codecov]

Codecov Report

Merging #22 (be6db48) into main (93d93c5) will decrease coverage by 1.55%.
The diff coverage is 100.00%.

@@             Coverage Diff             @@
##              main      #22      +/-   ##
===========================================
- Coverage   100.00%   98.44%   -1.56%     
===========================================
  Files           10       12       +2     
  Lines          427      580     +153     
===========================================
+ Hits           427      571     +144     
- Misses           0        9       +9     

Impacted Files	Coverage Δ
pennylane_orquestra/orquestra_device.py	100.00% <100.00%> (ø)
steps/expval.py	100.00% <100.00%> (ø)
steps/test_expval.py	91.42% <0.00%> (ø)

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[antalszava]

Not sure about the covearge drop: running make coverage-steps locally yields:

----------- coverage: platform linux, python 3.8.5-final-0 -----------
Name                   Stmts   Miss  Cover   Missing
----------------------------------------------------
steps/expval.py           46      0   100%
steps/test_expval.py     105      9    91%   211-212, 221-233
----------------------------------------------------
TOTAL                    151      9    94%
Coverage HTML written to dir coverage_html_report

(Note the test file is included for some reason.)