Enable STAR 96head partial tiprack pickup/drop + Fix requirement for A1 to have a tip

[BioCam]

Hi everyone,

The Problems

1. PLR on a STAR currently ALWAYS requires tiprack position A1 to have a tip (so it can retrieve that tip's information to calculate the correct z-coordinate for pickup)

2. We can only pick up full tipracks with the 96head, i.e. picking up partial tipracks (e.g. only the last 6 columns) is currently not possible with PLR.

PR Content

1. Instead of retrieving tip information from the tiprack based on hardcoded position "A1", PLR is already performing a check that there are tips in the tiprack and stores the tip instance handles in a list. I replaced the hardcoded "A1" dependency with the first element of the tip instance handle list.

2. The STAR uses the x_center-y_center position of its 96head "A1" probe (the part that houses the metal bearing, and picks up a tip) and is sent to any alignment_tipspot - so far this tipspot has been hardcoded to "A1" of the tiprack it picks up from.
   Here I am introducing the new STAR. pick_up_tips96() attribute alignment_tipspot: str = "A1".
   It's default is set to "A1", ensuring no change in existing behaviour and keeping the expected default behaviour (i.e. "full tiprack pickup").
   Setting it to a different Well identifier, e.g. "C3", would move the 96head to align its probe_A1 wit tipspot_C3, leading to a partial tiprack pickup.

TODOs

• this solution only accepts valid Well `identifiers! -> as a result the 96head can only offset to the right and to the bottom relative to the tiprack itself.
  i.e. offsetting to the top or left is currently not possible! (I am working on a separate solution to this and have left an Easter egg in the docstring to it, but it is a self-contained PR and needs a lot more testing)
• to ensure people don't accidentally use this new feature on a "framed/fenced" tiprack - which would result in a crash of the 96head probes into the tiprack - we will need to update the tipracks to include information about whether they are "framed/fenced" and raise an error if this is the case AND alignment_tipspot != "A1".

[BioCam]

Visual explainer of the above:

Note: the same concept works for aspirate/dispense, replace TipSpot with Well 👀
-> future PR