Use Match-Replace strategy to alias operators

[lukem12345]

Close #35

As a compromise between:

• considerations of computational efficiency
• warts relating to the types of "matched" variables destroying "context"
  , a "match & replace" strategy is adopted - inspired by AlgebraicRewriting - but using tight loops tailored to our workflow.

[codecov]

Codecov Report

Attention: Patch coverage is 79.41176% with 21 lines in your changes missing coverage. Please review.

Project coverage is 86.62%. Comparing base (261b0fb) to head (33630d6).

Files	Patch %	Lines
src/openoperators.jl	80.19%	20 Missing ⚠️
src/acset.jl	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #37      +/-   ##
==========================================
+ Coverage   85.15%   86.62%   +1.47%     
==========================================
  Files          12       13       +1     
  Lines         788      890     +102     
==========================================
+ Hits          671      771     +100     
- Misses        117      119       +2     

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[lukem12345]

I'll stick a pin in 03aa7ce as a complete version of this feature in an imperative/ database-manipulation manner.

I'll continue commits to this branch from the operadic composition approach.

[jpfairbanks]

Let's keep the other approach in separate files so that we can compare and contrast the changes. I'm thinking the repurposing of oapply will be much more maintainable long term.

[lukem12345]

Record of discussion with @GeorgeR227 :

• Take care that the RHS Decapodes are fully expanded
• Reformat (use newlines) in replace-operator functions
• Merge the "more imperative" code (after review process) in 03aa7ce. (It is more declarative than existing code currently in Decapodes.)
• Decide whether we should export the single-operator replacement functions.
• Even the oapply approach will need some imperativity on top of it, either creating RHS Decapodes on-the-fly with the names of the src/tgt variables, or in the LHS, and the replaced operator still has to be explicitly removed.

[lukem12345]

Default composition code has been cherry picked onto PR #52 . Upon that merging, I will reset this PR to 03aa7ce