Skip over identity ops in "lightning.qubit"

[maliasadi]

Context:
Fix issue #267.

[github-actions]

Test Report (C++) on Ubuntu

           1 files  ±0             1 suites  ±0   0s ⏱️ ±0s
       660 tests ±0         660 ✔️ ±0  0 💤 ±0  0 ❌ ±0 
228 174 runs  ±0  228 174 ✔️ ±0  0 💤 ±0  0 ❌ ±0 

Results for commit be6b795. ± Comparison against base commit 4c14421.

♻️ This comment has been updated with latest results.

[codecov]

Codecov Report

Merging #268 (1b97f31) into master (4c14421) will decrease coverage by 0.26%.
The diff coverage is 85.71%.

❗ Current head 1b97f31 differs from pull request most recent head be6b795. Consider uploading reports for the commit be6b795 to get more accurate results

@@             Coverage Diff             @@
##            master     #268      +/-   ##
===========================================
- Coverage   100.00%   99.73%   -0.27%     
===========================================
  Files            4        4              
  Lines          379      383       +4     
===========================================
+ Hits           379      382       +3     
- Misses           0        1       +1     

Impacted Files	Coverage Δ
pennylane_lightning/lightning_qubit.py	99.66% <83.33%> (-0.34%)	⬇️
pennylane_lightning/_version.py	100.00% <100.00%> (ø)

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[mlxd]

Nice one @maliasadi
Just left one comment, but happy to go with whatever you think works.