Optimize calldataload

[iamdefinitelyahuman]

What I did

Optimize how calldata is loaded into memory.

How I did it

Within optimizer.py, look for sequential instructions of e.g.

[mstore, 864, [calldataload, 4]],
[mstore, 896, [calldataload, 36]],
[mstore, 928, [calldataload, 68]],

This can be optimized to:

[calldatacopy 864, 4, 32 * 3]

The optimization is applied with the same logic we use to optimize memory-zeroing actions:

1. Look for sequential mstore instructions that reference sequential calldata locations.
2. Merge them into a single calldatacopy

How to verify it

Run the tests. I didn't add any new specific cases, but this optimization is applied anywhere multiple input args are taken by an external function so if it weren't working we'd see things failing everywhere.

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[codecov-io]

Codecov Report

Merging #2352 (b0033f7) into master (2eeb27f) will increase coverage by 0.04%.
The diff coverage is 98.27%.

@@            Coverage Diff             @@
##           master    #2352      +/-   ##
==========================================
+ Coverage   85.84%   85.89%   +0.04%     
==========================================
  Files          90       90              
  Lines        8791     8820      +29     
  Branches     2097     2103       +6     
==========================================
+ Hits         7547     7576      +29     
  Misses        755      755              
  Partials      489      489              

Impacted Files	Coverage Δ
vyper/optimizer.py	86.16% <98.27%> (+3.08%)	⬆️

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