fix(api): flex stacker store command should check labware configuration before hopper labware count

[ahiuchingau]

Overview

If you tried to store a labware in a stacker without previously setting the labware configuration, the protocol would fail with

CannotPerformModuleAction: Cannot store labware in Flex Stacker in slotName=<> because it is full

This is not true because there should be nothing in the stacker at this point. This PR fixes this misleading error by check that there's a labware configuration first, before validating the labware count in the hopper.

Test protocol

from opentrons.protocol_api import ProtocolContext, ParameterContext
from opentrons.protocol_api.module_contexts import (
    FlexStackerContext,
)

metadata = {
    "protocolName": "Flex Stacker DVT",
    "author": "Opentrons <protocols@opentrons.com>",
}
requirements = {
    "robotType": "Flex",
    "apiLevel": "2.24",
}


def run(protocol: ProtocolContext) -> None:
    """Protocol."""
    labware_name = "nest_96_wellplate_200ul_flat"
    labware_count = 3
    # ======================= SIMPLE SETUP ARRANGEMENT ======================
    stacker_A = protocol.load_module( "flexStackerModuleV1", "D4")
    stacker_A.set_stored_labware(
        load_name=labware_name,
        count=labware_count
    )
    
    stacker_B = protocol.load_module( "flexStackerModuleV1", "C4")

    labware_stack = stacker_A.retrieve()
    protocol.move_labware(labware_stack, stacker_B, True)
    stacker_B.store()

The error message should now make more sense:

FlexStackerLabwarePoolNotYetDefinedError: The Flex Stacker in slotName=<> has not been configured yet and cannot be filled.

[sfoster1]

Oops sorry!

Let's add a test though

[sfoster1]

Tests please

[sfoster1]

hooray! ty