Add ResourceHolder tutorial

docs/resources/resource-holder/resource-holder.ipynb

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+{
+ "cells": [
+  {
+   "cell_type": "markdown",
+   "id": "1fabc0d7",
+   "metadata": {},
+   "source": [
+    "# ResourceHolder\n",
+    "\n",
+    "`ResourceHolder` is a mixin class for resources that can hold exactly one other\n",
+    "resource. Examples include the sites of plate carriers which hold a single\n",
+    "plate, or the docking position of a module that accepts one plate or trough.\n",
+    "\n",
+    "`ResourceHolder` ensures that the child resource is placed correctly inside the\n",
+    "holder. When the holder is rotated the child resource is automatically shifted\n",
+    "so that its local origin lines up with the correct corner of the holder. This\n",
+    "avoids having to manually adjust coordinates for every rotation."
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "c71e1e1b",
+   "metadata": {},
+   "source": [
+    "## Why use a ResourceHolder?\n",
+    "\n",
+    "Many pieces of labware are designed to accommodate another resource at a\n",
+    "fixed position. A `PlateHolder` inside a carrier for example always contains\n",
+    "exactly one plate. The `ResourceHolder` abstraction models this behaviour.\n",
+    "It guarantees that only one resource is assigned at a time and exposes\n",
+    "convenient methods to work with the contained resource.\n",
+    "\n",
+    "By subclassing from `ResourceHolder` your own holder classes immediately gain\n",
+    "these behaviours without duplicating logic."
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "9e89a6c0",
+   "metadata": {},
+   "source": [
+    "## Basic usage"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "2a758652",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "from pylabrobot.resources import Resource, ResourceHolder\n",
+    "\n",
+    "holder = ResourceHolder(name=\"holder\", size_x=100, size_y=80, size_z=10)\n",
+    "plate  = Resource(name=\"plate\", size_x=100, size_y=80, size_z=15)\n",
+    "\n",
+    "holder.assign_child_resource(plate)\n",
+    "holder.resource.name"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "73233494",
+   "metadata": {},
+   "source": [
+    "After assignment the `resource` property returns the held item."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "4ae35102",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "holder.resource is plate"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "fbde07d7",
+   "metadata": {},
+   "source": [
+    "## Custom child location\n",
+    "\n",
+    "By default the child is positioned at the holder's origin. You can offset this\n",
+    "by passing ``child_location`` when constructing the holder."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "34a1b2b4",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "from pylabrobot.resources import Coordinate\n",
+    "\n",
+    "offset_holder = ResourceHolder(\n",
+    "    name=\"offset_holder\",\n",
+    "    size_x=100,\n",
+    "    size_y=80,\n",
+    "    size_z=10,\n",
+    "    child_location=Coordinate(x=10, y=5, z=0),\n",
+    ")\n",
+    "lid = Resource(name=\"lid\", size_x=95, size_y=75, size_z=5)\n",
+    "offset_holder.assign_child_resource(lid)\n",
+    "offset_holder.resource.location"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "6c54c505",
+   "metadata": {},
+   "source": [
+    "## Reassigning\n",
+    "\n",
+    "To replace the current child, call ``assign_child_resource`` again. The previous\n",
+    "child will be unassigned automatically."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "db3b133e",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "replacement = Resource(name=\"replacement\", size_x=100, size_y=80, size_z=15)\n",
+    "offset_holder.assign_child_resource(replacement)\n",
+    "offset_holder.resource.name"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "eb813c6a",
+   "metadata": {},
+   "source": [
+    "Attempting to assign another resource without allowing reassignment raises an\n",
+    "error."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "ece40649",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "try:\n",
+    "    holder.assign_child_resource(Resource(\"extra\", 10, 10, 10), reassign=False)\n",
+    "except ValueError as e:\n",
+    "    error_message = str(e)\n",
+    "error_message"
+   ]
+  }
+ ],
+ "metadata": {
+  "kernelspec": {
+   "display_name": "env",
+   "language": "python",
+   "name": "python3"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 5
+}