Significantly overhaul configuration management

Everything now uses bog-standard Python dataclasses, with Pydantic
providing validation and type conversion through separate classes using
its type adapter feature. It's also possible to define your classes
using Pydantic's own model type directly, making the type adapter
unnecessary, but I didn't want to do things that way because no actual
validation is needed when constructing a Song instance for example.
Having Pydantic do its thing only on-demand was preferable.

I tried a number of validation libraries before settling on Pydantic for
this. It's not the fastest option out there (msgspec is I think), but it
makes adding support for third-party types like yarl.URL really easy, it
generates a nice clean JSON Schema which is easy enough to adjust to my
requirements through its GenerateJsonSchema hooks, and raw speed isn't
all that important anyway since this is a single-user desktop program
that reads its configuration file once on startup.

Also, MessagePack is now mandatory if you're caching to an external
service. It just didn't make a whole lot sense to explicitly install
mpd-now-playable's Redis or Memcached support and then use pickling with
them.

With all this fussing around done, I'm probably finally ready to
actually use that configuration file to configure new features! Yay!

src/mpd_now_playable/config/schema.py

@@ -1,46 +1,5 @@
-from json import dump
-from pathlib import Path
-from pprint import pp
-from shutil import get_terminal_size
-from typing import Any, Mapping
-
-from apischema import schema, settings
-from apischema.json_schema import JsonSchemaVersion, deserialization_schema
-from apischema.schemas import Schema
-from class_doc import extract_docs_from_cls_obj
-
+from ..tools.schema.generate import write
 from .model import Config
 
-
-def field_base_schema(tp: type, name: str, alias: str) -> Schema | None:
-	desc_lines = extract_docs_from_cls_obj(tp).get(name, [])
-	if desc_lines:
-		print((tp, name, alias))
-		return schema(description=" ".join(desc_lines))
-	return None
-
-
-settings.base_schema.field = field_base_schema
-
-
-def generate() -> Mapping[str, Any]:
-	return deserialization_schema(
-		Config,
-		version=JsonSchemaVersion.DRAFT_7,
-	)
-
-
-def write() -> None:
-	schema = dict(generate())
-	schema["$id"] = Config.schema.human_repr()
-
-	schema_file = Path(__file__).parent / Config.schema.name
-	print(f"Writing this schema to {schema_file}")
-	pp(schema, sort_dicts=True, width=get_terminal_size().columns)
-	with open(schema_file, "w") as fp:
-		dump(schema, fp, indent="\t", sort_keys=True)
-		fp.write("\n")
-
-
 if __name__ == "__main__":
-	write()
+	write(Config)