Initial DeriveUnit implementation

This contains the initial DeriveUnit implementation, including signature
validation, this initial implentation only supports ValueDescriptors in
the signature alongside the SignalDescriptor and returns a single
ValueDescriptor

The worker thread still needs to be defined and started but the offline
processing has already been validate to work as a first prototype

test/manual/derive_unit.py

@@ -0,0 +1,41 @@
+from uuid import uuid4
+from dynalab_core.derive import DeriveUnit
+from dynalab_core.protocols.packets.data import ValueDescriptor
+from dynalab_core.protocols.packets.handshake import SignalDescriptor
+
+
+def process(
+    a: ValueDescriptor,
+    b: ValueDescriptor,
+    r: SignalDescriptor,
+) -> ValueDescriptor:
+    val = ValueDescriptor(
+        signal_id=r.id, value=a.value + b.value, timestamp=a.timestamp
+    )
+    return val
+
+
+sig_a = SignalDescriptor(
+    id=uuid4(),
+    name="Signal A",
+    type="number",
+)
+
+sig_b = SignalDescriptor(
+    id=uuid4(),
+    name="Signal A",
+    type="number",
+)
+
+sig_r = SignalDescriptor(
+    id=uuid4(),
+    name="Signal R",
+    type="number",
+)
+
+unit = DeriveUnit(uuid4(), process, [sig_a, sig_b], sig_r)
+
+val_a = ValueDescriptor(signal_id=sig_a.id, value=1, timestamp=0)
+val_b = ValueDescriptor(signal_id=sig_a.id, value=2, timestamp=10)
+
+print(unit.process_offline([val_a, val_b]))