Add liquid handling capabilities

LiquidHandlingCapability: faithful port of legacy LiquidHandler frontend
with tip tracking (commit/rollback), volume tracking, ChannelizedError
handling, tip presence probing, can_pick_up_tip validation, spread modes,
BlowOutVolumeError, and convenience methods (return_tips, discard_tips,
transfer, move_tips, use_channels, use_tips). BackendParams passed through
all backend calls and composition methods with operation-specific names.

Head96Capability: 96-head operations with tip tracking (commit/rollback),
volume tracking, partial tip pickup, single-container (trough) support,
container size validation, and convenience methods (return_tips,
discard_tips, stamp). State serialization on both capabilities.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: rickwierenga

pylabrobot/capabilities/liquid_handling/__init__.py

@@ -0,0 +1,18 @@
+from .pip_backend import PIPBackend
+from .errors import ChannelizedError, NoChannelError
+from .head96 import Head96Capability
+from .head96_backend import Head96Backend
+from .pip import PIP
+from .standard import (
+  Aspiration,
+  Dispense,
+  DropTipRack,
+  Mix,
+  MultiHeadAspirationContainer,
+  MultiHeadAspirationPlate,
+  MultiHeadDispenseContainer,
+  MultiHeadDispensePlate,
+  Pickup,
+  PickupTipRack,
+  TipDrop,
+)

pylabrobot/capabilities/liquid_handling/errors.py

@@ -0,0 +1,26 @@
+"""Errors for liquid handling operations."""
+
+from typing import Dict
+
+
+class NoChannelError(Exception):
+  """Raised when no channel is available."""
+
+
+class BlowOutVolumeError(Exception):
+  """Raised when blow-out air volume is invalid."""
+
+
+class ChannelizedError(Exception):
+  """Raised by multi-channel operations. Contains per-channel errors."""
+
+  def __init__(self, errors: Dict[int, Exception], **kwargs):
+    self.errors = errors
+    self.kwargs = kwargs
+
+  def __str__(self) -> str:
+    kwarg_string = ", ".join([f"{k}={v}" for k, v in self.kwargs.items()])
+    return f"ChannelizedError(errors={self.errors}, {kwarg_string})"
+
+  def __len__(self) -> int:
+    return len(self.errors)