Optimise x86_64 builds with AVX friendly opts

[mlxd]

Context: This enables AVX operations by default for Intel/AMD machines which can improve performance of vectorisable operations.

Description of the Change: AVX support is added to Linux x86_64 wheels. In addition, the width of various registers is reduced for many parametric ops by explicitly favouring 64-bit wide operations instead of 128-bit (T vs std::complex<T>) where applicable.

Benefits: Improves overall runtime performance.

Possible Drawbacks: Machines not supporting AVX (pre-2011) will require manual builds to run lightning.

Related GitHub Issues:

[github-actions]

Hello. You may have forgotten to update the changelog!
Please edit .github/CHANGELOG.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 #157 (0c52a24) into master (7c390d3) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##            master      #157   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            4         4           
  Lines          182       182           
=========================================
  Hits           182       182           

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[github-actions]

Test Report (C++) on Ubuntu

       1 files  ±0         1 suites  ±0   0s ⏱️ ±0s
   327 tests ±0     327 ✔️ ±0  0 💤 ±0  0 ❌ ±0 
1 185 runs  ±0  1 185 ✔️ ±0  0 💤 ±0  0 ❌ ±0 

Results for commit 0c52a24. ± Comparison against base commit 7c390d3.

♻️ This comment has been updated with latest results.

[trevor-vincent]

Awesome work Lee. I see no issues!