Performance/improve render caching, fix unitialized variable use

[m-m-adams]

Significant improvement in voices by tagging likely/unlikely branches. Can likely improve a lot more by caching some repeated checks.

Also removes rendering directly to the output buffer - the extra time to check and set up for that is worse than an extra memcpy

Fixes a bug where stereo wavefolding used the non-anti aliased fold function

same before as here - #2199

Synth after:

Multisample after:

[github-actions[bot]]

Test Results

56 tests  +8   56 :white_check_mark: +8   0s :stopwatch: ±0s  9 suites ±0    0 :zzz: ±0   9 files   ±0    0 :x: ±0 

Results for commit c183d8bd. ± Comparison against base commit 99281139.

:recycle: This comment has been updated with latest results.