Moved derive unit API to DLUnit

Derived units now use a DLUnit class similar to a DLPak to be easily
stored and loaded, the public API has been updated to either take a
DLUnit object or a Path where it reads the DLUnit from a *.dlunit file

The .dlunit file is a ZIP compressed archive containing two files, a
manifest.json which stores the units uuid, its input signals and its
output signal, and unit.py which is the python code for the unit, the
same rules apply (one python function with a specifically structured
signature) as when a string was passed in the old API

Errors have been added to have a DLUnitError similar to the DLPakError
as the DLUnit class is heavily inspired from the DLPak architecutre

Logging may still be primitive, this will be covered in the next AI
logging sweep to homogenize and clean up the logging aspect of things

src/dynalab_core/dlunit.py

@@ -0,0 +1,142 @@
+# Copyright (C) 2026 Hector van der Aa <hector@h3cx.dev>
+# Copyright (C) 2026 Association Exergie <association.exergie@gmail.com>
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+import logging
+from pathlib import Path
+from typing import Literal, Self
+from uuid import UUID
+from zipfile import ZIP_DEFLATED, ZipFile
+
+from pydantic import BaseModel, Field
+
+from dynalab_core.errors import DLPakError, DLUnitError
+from dynalab_core.protocols.packets.handshake import SignalDescriptor
+
+
+log = logging.getLogger(__name__)
+
+
+class DeriveManifest(BaseModel):
+    unit_uuid: UUID
+    input_signals: list[SignalDescriptor] = Field(default_factory=list)
+    return_signal: SignalDescriptor
+    comments: str = ""
+
+
+class DLUnit:
+    def __init__(self) -> None:
+        self._dir: Path | None = None
+        self._filename: str | None = None
+        self._savetype: Literal["zip", "folder"] = "zip"
+        self._data: str | None = None
+        self._manifest: DeriveManifest | None = None
+
+    def set_data(self, data: str) -> None:
+        self._data = data
+
+    def set_manifest(
+        self,
+        unit_uuid: UUID,
+        input_signals: list[SignalDescriptor],
+        return_signal: SignalDescriptor,
+    ) -> None:
+
+        self._manifest = DeriveManifest(
+            unit_uuid=unit_uuid,
+            input_signals=input_signals,
+            return_signal=return_signal,
+        )
+
+    def read(self, file: str | Path) -> Self:
+        input_path = Path(file)
+
+        try:
+            with ZipFile(input_path, mode="r") as archive:
+                manifest = DeriveManifest.model_validate_json(
+                    archive.read("manifest.json")
+                )
+                data: str = archive.read("unit.py").decode("utf-8")
+        except Exception as error:
+            log.exception(
+                "Failed to read DLUnit archive from %s",
+                input_path.name,
+                extra={
+                    "event": "dlunit.read_failed",
+                    "input_filename": input_path.name,
+                    "exception_type": type(error).__name__,
+                },
+            )
+            raise DLUnitError(
+                f"Could not read DLUnit archive {input_path}: {error}",
+                code="read_failed",
+            ) from error
+
+        self._dir = input_path.parent
+        self._filename = input_path.name
+        self._data = data
+        self._manifest = manifest
+
+        log.info(
+            "Read DLUnit archive from %s",
+            input_path.name,
+            extra={
+                "event": "dlunit.read",
+                "input_filename": input_path.name,
+            },
+        )
+        return self
+
+    def write(self, dir: str | Path, filename: str) -> None:
+        output_dir = Path(dir)
+
+        if self._data is None:
+            raise DLUnitError(
+                "Cannot write a DLUnit archive before setting its data",
+                code="no_data",
+            )
+        if self._manifest is None:
+            raise DLUnitError(
+                "Cannot write a DLUnit archive before creating its manifest",
+                code="no_manifest",
+            )
+
+        if output_dir.is_file():
+            output_dir = output_dir.parent
+
+        file_path = Path(filename)
+
+        if file_path.suffix.lower() != ".dlunit":
+            file_path = file_path.with_suffix(".dlunit")
+
+        output_path = output_dir / file_path
+
+        try:
+            with ZipFile(output_path, mode="w", compression=ZIP_DEFLATED) as archive:
+                archive.writestr(
+                    "manifest.json", self._manifest.model_dump_json(indent=2)
+                )
+                archive.writestr("unit.py", self._data.export_csv())
+        except Exception as error:
+            log.exception(
+                "Failed to write DLUnit archive to %s",
+                output_path.name,
+                extra={
+                    "event": "dlunit.write_failed",
+                    "output_filename": output_path.name,
+                    "exception_type": type(error).__name__,
+                },
+            )
+            raise DLUnitError(
+                f"Could not write DLUnit archive {output_path}: {error}",
+                code="write_failed",
+            ) from error
+
+        log.info(
+            "Wrote DLUnit archive to %s",
+            output_path.name,
+            extra={
+                "event": "dlunit.written",
+                "output_filename": output_path.name,
+            },
+        )