Micro-optimize and memoize BitPat.rawString

[jackkoenig]

BitPat.rawString is called a lot when decoding and is used for certain
BitPat operations. We should use it less but this is at least a bandaid.

@sequencer, have you noticed issues with this?

Contributor Checklist

• Did you add Scaladoc to every public function/method?
• Did you add at least one test demonstrating the PR?
• Did you delete any extraneous printlns/debugging code?
• Did you specify the type of improvement?
• Did you add appropriate documentation in docs/src?
• Did you state the API impact?
• Did you specify the code generation impact?
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Type of Improvement

• performance improvement

API Impact

No impact, this should be source and binary compatible

Backend Code Generation Impact

None

Desired Merge Strategy

Squash

Release Notes

Micro-optimize and memoize BitPat.rawString to speed up decoding APIs

Reviewer Checklist (only modified by reviewer)

• Did you add the appropriate labels?
• Did you mark the proper milestone (Bug fix: 3.4.x, [small] API extension: 3.5.x, API modification or big change: 3.6.0)?
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[sequencer]

@sequencer, have you noticed issues with this?

Sorry, I didn't test the performance issue in the Scala side, I will take care of those in the future. For most of the time, I have been using pure functional paradigm, however when it comes to these cases, the performance will be embarrassing... Sorry about that.