Add GraphLayer layout redraw throttling

[ibgreen]

Summary

• add GraphLayer.layoutUpdateInterval to throttle layout-driven redraws without suppressing layout lifecycle callbacks
• clear pending throttled redraw timers when the layer finalizes or swaps graph engines
• document the public prop in the GraphLayer API reference and v9.4 notes

Classification

Feature / public API addition for graph-layers rendering cadence. It affects internal redraw scheduling, not a rendered docs/example route.

Validation

• yarn
• yarn test-node modules/graph-layers/test/layers/graph-layer.spec.ts
• yarn test-node modules/graph-layers/test
• yarn lint-fix
• yarn lint
• yarn build
• cd website && yarn && yarn build
• pre-commit yarn test

Visual proof

Not applicable. This PR changes GraphLayer redraw scheduling and public API docs; it is covered by fake-timer unit tests plus package/website builds rather than a user-visible route or interaction recording.

Residual risk

Low to medium. The default remains 0, preserving current every-layout-change redraw behavior. Nonzero intervals coalesce intermediate redraws, so consumers using the new prop should expect visual updates at the requested cadence while lifecycle callbacks still fire.

[github-actions]

Coverage

Stmts: 51.02% ▲+0.21% | Branch: 41.94% ▲+0.02% | Funcs: 49.23% ▲+0.03% | Lines: 51.16% ▲+0.21%

Test Files 164 passed (164)