fix(templates/wasm): $WRK was modified by stereo oscillators, messing up all modulations targeting units after the unit

add also tests to make sure we don't mess it up again

tests/test_oscillat_gainmod_stereo.yml

@@ -0,0 +1,43 @@
+bpm: 100
+rowsperbeat: 4
+score:
+    rowsperpattern: 16
+    length: 1
+    tracks:
+        - numvoices: 1
+          order: [0]
+          patterns: [[80, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0]]
+patch:
+    - numvoices: 1
+      units:
+        - type: envelope
+          parameters: {attack: 80, decay: 80, gain: 128, release: 80, stereo: 0, sustain: 64}
+        - type: oscillator
+          parameters: {color: 128, detune: 64, gain: 32, lfo: 0, phase: 0, shape: 64, stereo: 0, transpose: 64, type: 0, unison: 0}
+          id: 1
+        - type: oscillator
+          parameters: {color: 128, detune: 62, gain: 32, lfo: 0, phase: 0, shape: 64, stereo: 1, transpose: 64, type: 0, unison: 0}
+          id: 2
+        - type: addp
+          parameters: {stereo: 0}
+        - type: addp
+          parameters: {stereo: 0}
+        - type: oscillator
+          parameters: {color: 128, detune: 60, gain: 32, lfo: 0, phase: 0, shape: 64, stereo: 0, transpose: 64, type: 0, unison: 0}
+          id: 3
+        - type: addp
+          parameters: {stereo: 0}
+        - type: mulp
+          parameters: {stereo: 0}
+        - type: push
+          parameters: {stereo: 0}
+        - type: oscillator
+          parameters: {color: 128, detune: 64, gain: 128, lfo: 1, phase: 64, shape: 64, stereo: 0, transpose: 70, type: 0, unison: 0}
+        - type: send
+          parameters: {amount: 68, port: 5, sendpop: 0, stereo: 0, target: 1}
+        - type: send
+          parameters: {amount: 68, port: 5, sendpop: 0, stereo: 0, target: 2}
+        - type: send
+          parameters: {amount: 68, port: 5, sendpop: 1, stereo: 0, target: 3}
+        - type: out
+          parameters: {gain: 128, stereo: 1}