fix(🎨): honor the optional paint and blend mode in drawPatch

[tahakocal]

Description

SkCanvas.drawPatch declares both mode and paint as optional:

drawPatch(cubics, colors?, texs?, mode?: BlendMode | null, paint?: SkPaint): void

Neither implementation accepted their absence. Fixes #4062.

Native (cpp/api/JsiSkCanvas.h):

• the paint was taken from arguments[4] whenever count >= 4, so a four-argument call read one slot past the end of the JSI argument array, and the resulting null shared_ptr was then dereferenced — a hard crash rather than an exception;
• the blend mode used an unconditional arguments[3].asNumber(), which throws for a null or omitted mode (and reads out of bounds for calls with fewer than four arguments).

Web (src/skia/web/JsiSkCanvas.ts): the missing paint was forwarded to CanvasKit as undefined, which throws TypeError: Cannot read properties of undefined (reading 'Fd').

Both layers now fall back to a default-constructed paint and to SkBlendMode::kModulate, matching the four-argument SkCanvas::drawPatch overload and CanvasKit's own shim (t || (t = BlendMode.Modulate)). The web fallback is a raw new CanvasKit.Paint() rather than Skia.Paint(), because the latter enables antialiasing and would not match a default-constructed SkPaint natively; it is released in a finally.

drawAtlas has the same class of bug: its blend mode lives at index 4 but was guarded by count > 5, so a five-argument call silently dropped it. Worth noting for reviewers: this one is not observable today — Skia ignores the atlas blend mode when no colors array is supplied, and a call that supplies colors already has count >= 6. I verified this against CanvasKit (Src vs Plus vs Clear with no colors produce byte-identical output; with colors they differ). The guard was still off by one, so it is corrected here.

The declarative renderer is unaffected: sksg/Recorder/commands/Drawing.ts always passes all five arguments to drawPatch and all seven to drawAtlas.

Test plan

Two tests added to renderer/__tests__/e2e/CoonPatch.spec.tsx, so they run against CanvasKit locally and against the device in E2E:

1. drawPatch(cubics, colors) must render pixel-identically to the explicit drawPatch(cubics, colors, null, BlendMode.Modulate, paint) with a default (non-antialiased) paint. Fails before the change with the TypeError above.
2. With a shader paint and texture coordinates — where the patch blend mode is observable — an omitted mode must match an explicit BlendMode.Modulate, while BlendMode.SrcOver must differ. The second assertion keeps the first one honest.

yarn jest src/renderer/__tests__/e2e/CoonPatch.spec.tsx src/renderer/__tests__/e2e/Atlas.spec.tsx src/skia/__tests__/ZeroValues.spec.ts
Test Suites: 3 passed, 3 total
Tests:       26 passed, 26 total

Full package suite, tsc --noEmit and eslint --max-warnings 0 are clean. Additional verification on the web path: all six previously-throwing argument shapes (2/3/4 args, mode null, paint undefined, paint null) now match the reference rendering exactly (0 of 16384 bytes differ); the shapes that already worked are byte-for-byte unchanged; 40k calls grow CanvasKit.HEAPU8 by 0 bytes, and a drawPatch that throws leaves the canvas usable.

I could not build the native side locally, so the C++ change is covered by review and by the added E2E tests rather than by a local device run.

[tahakocal]

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