Include test suite in coverage

[trbromley]

The tests from PennyLane's device test suite will now be included when generating coverage reports. The makefile has also been updated to make using the test suite easier.

As we further modify some of the default.qubit-inherited methods in lightning.qubit, it'll be useful to harness the test suite tests for coverage so we don't have to replicated existing tests.

[github-actions]

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[github-actions]

Test Report (C++) on Ubuntu

    1 files  ±0      1 suites  ±0   0s ⏱️ ±0s
118 tests ±0  118 ✔️ ±0  0 💤 ±0  0 ❌ ±0 
370 runs  ±0  370 ✔️ ±0  0 💤 ±0  0 ❌ ±0 

Results for commit e309d44. ± Comparison against base commit e309d44.

♻️ This comment has been updated with latest results.

[codecov]

Codecov Report

Merging #123 (cac37ee) into master (2b26841) will increase coverage by 1.85%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           master      #123      +/-   ##
===========================================
+ Coverage   98.14%   100.00%   +1.85%     
===========================================
  Files           3         3              
  Lines          54        54              
===========================================
+ Hits           53        54       +1     
+ Misses          1         0       -1     

Impacted Files	Coverage Δ
pennylane_lightning/lightning_qubit.py	100.00% <0.00%> (+2.04%)	⬆️

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[mlxd]

Great idea and good job on this @trbromley !