v1 STAR and Prep tip commands: a rack no head can reach is refused

[BioCam]

The Problem

The legacy LiquidHandler refuses to pick up from, or drop into, a tip rack with a lid on or with another rack standing on it (#1288). The v1 STAR and Prep drivers do not: handed the bottom rack of a stack of four nested racks, pick_up_tips sends the command, on the channels and on the 96-head. The check behind legacy's refusal is TipRack._available_for_tip_handling, a private property, so no driver and no library function may ask it - which is also why find_tip_spots (#1381) returns spots from every rack of a stack, covered ones included.

PR Content/Solution

• TipRack.available_for_tip_handling, public: a rack is available when it is placed, has no lid on, and no other rack stands on it in its z-growing stack. Only "placed" is new; the rest is StandingTipRack: a tip rack that stands on its own, and can nest in a stack #1288's check
• the private name is gone, two weeks after it went in and before any release carried it; legacy's one caller reads the public property
• check_tip_racks_available(tip_spots, action) in resources.tip_rack raises ValueError for a rack that is not available, asking each rack once
• pick_up_tips and drop_tips call it before anything is sent: Pipettes and Head96 on the STAR, Pipettes and Head8 on the Prep. return_tips, the tip presence probes and consolidate_tip_inventory go through them
• find_tip_spots(..., available_for_tip_handling=...), a selection argument like has_tip: True for spots in racks a head can reach, False for the others, None for both. None is the default and it is the last argument, so every existing call returns what it did

stack = ResourceStack("ntr_stack", "z")
carrier[0] = stack
for level in range(4):
  stack.assign_child_resource(hamilton_96_tiprack_300uL_NTR(name=f"ntr_{level}"))

await star.head96.pick_up_tips(deck.get_resource("ntr_0"))
# on main: C0EP is sent
# here: ValueError: Cannot pick up tips from 'ntr_0': it is not available for tip handling.

find_tip_spots(deck, has_tip=True, count=8, x_aligned=True, available_for_tip_handling=True)  # ntr_3

Tests: pipettes_tests and head_tests on the STAR, pipettes_tests and head8_tests on the Prep - a rack with a lid on is refused for pick-up and for drop, and nothing is sent; tip_rack_tests - a rack placed nowhere is not available; tip_spot_finding_tests - on a stack of two racks None gives both racks' spots, True the top rack's, False the lower one's.

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