Changes to support hyperion 1283 use pixels per micron from file not gda

[rtuck99]

Fixes (DiamondLightSource/hyperion#1283)

Add microns-per-pixel to the snapshot so that oav snapshot events can contain data needed for ispyb
A small change to OAV initialiser to allow parameters to be specified on construction for system tests

Checks for reviewer

• Would the PR title make sense to a scientist on a set of release notes
• If a new device has been added does it follow the standards

[d-perl]

Just one nitpick, up to you

[d-perl]

Nit: the default arg will be evaluated at definition time (i.e. on import). I know that just stores the paths, but I'd still rather do something like:

@skip_device(lambda: BL == "s03")
def oav(
    wait_for_connection: bool = True,
    fake_with_ophyd_sim: bool = False,
    params: OAVConfigParams | None = None,
) -> OAV:
    """Get the i03 OAV device, instantiate it if it hasn't already been.
    If this is called when already instantiated in i03, it will return the existing object.
    """
    return device_instantiation(
        OAV,
        "oav",
        "",
        wait_for_connection,
        fake_with_ophyd_sim,
        params=params or OAVConfigParams(ZOOM_PARAMS_FILE, DISPLAY_CONFIG),
    )

In case the OAVConfigParams ever changes to do something in its init

[rtuck99]

I'll make the change, although I think most classes should not do anything interesting in constructors, especially parameter classes.