* WebAssembly ABI 2: neighbouring frames for effect plug-ins (#2773)
A wasm plug-in can export ec_api_version 2 and ec_render2 to receive the layer's previous and next frames, their layer times and validity flags. Neighbours come from PluginHost::input_at, are resampled onto the current grid, and are zeroed when absent. ABI 1 modules (ec_render) load and render unchanged; the manifest api stays independent. A layer with an ABI 2 plug-in keys the render cache on layer time; the Plug-in Library accepts ABI 1-2 releases. Docs, help text and tests updated.
* Fix ABI 2 neighbour times on NTSC frame boundaries
ime * fps is often a few ulps off an integer at rates such as 24000/1001. The old boundary test then took the bracket branch and passed the current frame back as prev (or
ext). Treat a near-integer as a frame boundary within 1e-6 frames, and test 2400 frames at 24000/1001: every boundary must get the frames either side. Also document the loader helpers for the docstring coverage check.
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Co-authored-by: justanshh <294019246+justanshh@users.noreply.github.com>
