PitchWalker was classified as a generator but always consumed the
incoming pattern's triggers. Reclassify as a processor so it modifies
the pattern produced by an upstream generator (clonePattern instead of
createPattern). Add reEvalOnLoop flag on the Primitive base class; when
set, the sequencer re-evaluates the chain at each loop start so
stateful primitives produce evolving patterns across loops.
Replace the pitch*127 encoding hack with a dedicated midiNote field on
pattern steps. IntervalLock now writes integer MIDI notes to step.midiNote
while preserving the original [0,1] pitch for other consumers. The clock
and sequencer bridge pass midiNote through the event pipeline.
Also reworks mergePatterns to be trigger-aware: when only one generator
fires at a step, use its values directly instead of averaging with the
other generator's defaults.
