Create records for appending tables

[coretl]

In v4.0 of PandABlocks-server we have MODE and QUEUED_LINES attributes:
https://pandablocks.github.io/PandABlocks-server/master/fields.html

After PandABlocks/PandABlocks-client#107 there will be a has_mode attribute in the TableFieldInfo that tells us we have these fields. This ticket is to add some FastCS attributes when has_mode==True to allow table streaming.

At the moment we create a single Attribute for the table value:

fastcs-PandABlocks/src/fastcs_pandablocks/panda/blocks/blocks.py

Lines 357 to 372 in f2bf17e

	def _make_table_field(
	self,
	parent_block: BlockController,
	panda_name: PandaName,
	field_info: TableFieldInfo,
	):
	structured_datatype = [
	(name, self._table_datatypes_from_table_field_details(details))
	for name, details in field_info.fields.items()
	]
	# TODO: Add units handler to update the units field and value of this one PV
	# https://github.com/PandABlocks/PandABlocks-ioc/blob/c1e8056abf3f680fa3840493eb4ac6ca2be31313/src/pandablocks_ioc/ioc.py#L750-L769
	parent_block.attributes[panda_name.attribute_name] = AttrRW(
	Table(structured_datatype),
	handler=TableFieldHandler(panda_name),
	)

The new list of attributes for a table with has_mode==True is:

• panda_name + PandaName(sub_field="NEXT_WRITE") a WO enum of Replace / Append / Append Last that says what the next write to the table value will do
• panda_name is the RW table value as before
• panda_name + PandaName(sub_field="CLEAR") a command that sends an empty table to PandA
• panda_name + PandaName(sub_field="MODE") is the RO current table mode, one of INIT / FIXED /STREAMING / STREAMING_LAST whose value is supplied from the PandA field {block_name}.{field_name}.MODE
• panda_name + PandaName(sub_field="QUEUED_LINES") is the RO current number of table lines not yet processed by the FPGA whose value is supplied from the PandA {block_name}.{field_name}.QUEUED_LINES

Acceptance Criteria

• The attributes added and tests added