Remove AC matching

[HarrisonGrodin]

It seems like numerous performance issues can be attributed to the costliness of AC pattern matching.

The match function is called for every application of a pattern-based rule on every subterm of every intermediate term. Thus, matching clearly must be efficient during normalization - for example, a recent coverage build shows that over the course of the test suite, we:

• call the top-level match method 4 million times
• call associative matching 1 million times
• call commutative matching 280k times
• construct nearly 7 million Match objects

In addition to the algorithmic complexity associated with associative and commutative matching, allowing for the storage of multiple matches using nested data structures increases the number of allocations performed. Additionally, the use of this specialized algorithm in such a fundamental procedure severely limits our ability to apply other modern research techniques to Rewrite.

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This PR removes AC pattern matching, substituting it for more performant normalization strategies when AC is necessary.

• Remove AC pattern matching
• Add custom rules reimplementing the functionalities where necessary

[HarrisonGrodin]

cc: @MasonProtter

[HarrisonGrodin]

How do we want to handle normalization of AC operators? Explicit lazy AC matching?