Remove cumulative paint layer limit

[VladimirKras]

Motivation

Dense scenes silently stop emitting requested clip and effect layers once cumulative painting crosses the nominal 1,024-layer limit, so later content is painted with the wrong layer stack and becomes visibly corrupted even when frame rate is healthy. The cap is enforced in backend-independent paint code, so it affects CPU and GPU renderers alike.

Why the cap can be removed

The cap was introduced at 28 in 596d419 as a workaround for Vello #644, then raised to 1,024 in c74b019. Vello fixed the underlying empty-clip encoding bug in Vello #651, merged in August 2024; Blitz now uses Vello 0.10.0, so retaining the old global workaround causes silent data loss without protecting current renderers from that historical bug.

Changes

• Remove the cumulative layer cap and its now-unused accounting.

Validation

• cargo test -p blitz-paint --lib
• cargo clippy -p blitz-paint --no-deps -- -D warnings
• cargo fmt --all -- --check
• git diff --check

The workspace Clippy command currently stops on an unrelated existing needless_return warning at packages/blitz-dom/src/mutator.rs:1218 with Rust 1.96.1; the affected crate passes Clippy with dependency linting disabled.

Note

AI-assistance disclosure: this change and PR description were prepared with assistance from Codex/GPT-5 and reviewed by the submitter.

WPT results

No changes in test results compared to main.

_{Generated by the WPT workflow.}

[nicoburns]

This seems reasonable, but can we ditch the test please.

Vello Classic and Vello Hybrid both still have issues with resource allocation, but this isn't really guarding against it effectively.

[VladimirKras]

Sorry about the useless test. Dropped it.