perft: lazy render model after event loop

[aymanbagabas]

On a large program, this can reduce repeated model render calls when the model is getting updated rapidly. This change makes the model stored as an atomic pointer for safe concurrent access between the event loop and the render loop.

The model is now stored internally as an atomic pointer, and updated after each event loop iteration. The render loop reads the latest model from the atomic pointer before rendering its View.

Benchmarks show a slight reduction in allocations for the TeaTest example.

goos: darwin
goarch: arm64
pkg: github.com/charmbracelet/bubbletea/v2
cpu: Apple M3 Max
          │   old.txt   │            new.txt            │
          │   sec/op    │   sec/op     vs base          │
TeaRun-16   321.2µ ± 3%   318.3µ ± 4%  ~ (p=0.247 n=10)

          │   old.txt    │            new.txt             │
          │     B/op     │     B/op      vs base          │
TeaRun-16   623.0Ki ± 0%   622.2Ki ± 0%  ~ (p=0.105 n=10)

          │   old.txt   │              new.txt               │
          │  allocs/op  │  allocs/op   vs base               │
TeaRun-16   1.837k ± 0%   1.828k ± 0%  -0.52% (p=0.000 n=10)

[codecov]

Codecov Report

❌ Patch coverage is 64.28571% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 53.28%. Comparing base (4accb1c) to head (3734655).

Files with missing lines	Patch %	Lines
tea.go	64.28%	4 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           v2-exp    #1532      +/-   ##
==========================================
+ Coverage   52.88%   53.28%   +0.40%     
==========================================
  Files          24       24              
  Lines        1180     1186       +6     
==========================================
+ Hits          624      632       +8     
+ Misses        477      475       -2     
  Partials       79       79              

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[aymanbagabas]

Actually, this might not be a good idea because it will significantly slow down since it synchronizes the event and render loop which we don't want here :/
Closing...