Draft of SQLAlchemy-based EntryCollection

[ml-evs]

Based on the initial work by @jensj at https://gitlab.com/jensj/ase-optimade, this PR introduces a SQLAlchemy-based backend for the reference server. This collection is intended to be used "from scratch", by e.g., ingesting OPTIMADE data into a new set of tables, rather than attaching to an existing database of a given format. It has no corresponding filter transformer class as filtering requires access to the table metadata, so as such, it is bundled as part of the collection.

Still very WIP and currently only handles structure data (not links etc).

[codecov]

Codecov Report

Merging #1656 (445d714) into master (03ab81e) will decrease coverage by 3.94%.
The diff coverage is 0.95%.

@@            Coverage Diff             @@
##           master    #1656      +/-   ##
==========================================
- Coverage   91.04%   87.11%   -3.94%     
==========================================
  Files          74       75       +1     
  Lines        4580     4787     +207     
==========================================
  Hits         4170     4170              
- Misses        410      617     +207     

Flag	Coverage Δ
project	87.11% <0.95%> (-3.94%)	⬇️
validator	87.00% <0.95%> (-3.94%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
optimade/server/entry_collections/sqlalchemy.py	0.00% <0.00%> (ø)
optimade/server/config.py	93.75% <100.00%> (+0.13%)	⬆️

... and 1 file with indirect coverage changes

[blokhin]

Isn't this a filter transformer?

optimade-python-tools/optimade/server/entry_collections/sqlalchemy.py

Lines 369 to 390 in 445d714

	def parse_lark_tree(node: Tree | Token) -> Any:
	"""Convert Lark tree to simple data structure.
	See examples in ``parser_test.py``.
	"""
	if isinstance(node, Token):
	if node.type == "SIGNED_INT":
	return int(node.value)
	if node.type == "SIGNED_FLOAT":
	return float(node.value)
	if node.type == "ESCAPED_STRING":
	return node.value[1:-1]
	return (node.type, node.value)
	children = [parse_lark_tree(child) for child in node.children] # type: ignore
	if len(children) == 1:
	return children[0]
	if node.data == "expression":
	return ("OR", children)
	if node.data == "expression_clause":
	return ("AND", children)
	return children