Fix three performance traps in the OFX plugin preview pipeline that
caused slideshow-like performance when any plugin was active.
1. Eliminate per-frame PluginRenderer creation (GL FBO alloc/free)
RenderProcessor is stack-allocated per ticket, so its
plugin_renderer_ member was constructed and destroyed every frame.
PluginRenderer inherits OpenGLRenderer, whose PostInit() calls
glGenFramebuffers() and whose destructor calls glDeleteFramebuffers().
On Apple Silicon's TBDR this is pathologically expensive.
Fix: use a thread_local cached PluginRenderer so each render thread
creates it only once and reuses it forever.
2. Call getClipPreferences() conditionally
The code unconditionally called instance->getClipPreferences() on
every single frame. This dispatches kOfxImageEffectActionGetClipPreferences
into the plugin even when no inputs or parameters have changed.
Fix: check areClipPrefsDirty() first. The OpenFX Host Support library
already tracks this flag and sets it to true when slave params or clip
connections change.
3. Call ApplyParamOverrides() before renderAction
ApplyParamOverrides() was defined but never invoked, so animated
plugin parameters were never pushed into the OFX instance before
rendering.
Fix: call it after beginRenderAction() and before renderAction(),
injecting the current NodeValueRow values at the correct OfxTime.
Mike-Solar
ff0eee3a88