feat: add function to calculate dynamic default Actor memory (#570)

This PR introduces the logic to calculate a dynamic default Actor memory
limit based on a provided expression string.

**TL;DR:**
- Uses a sandboxed MathJS instance to securely evaluate expressions.
- Supports `{{variable}}` placeholders with strict validation: `input.*`
paths are allowed, while `runOptions.*` keys are strictly
whitelisted(only 7 variables allowed).
- Injects the Actor input and run options into the evaluation scope.
- Adds a custom `get(obj, path, default)` helper to safely access nested
properties without crashing on missing paths (e.g., `get(input,
'startUrls.length', 0)`).
- Rounds the evaluated result to the closest valid power-of-2 memory
tier. Result is clamped to min/max range. (128MB-32GB)

Note: when using this function in our API, we'll use it in
`worker_thread`. I didn't add worker_thread to this package, because I
suppose it can be used from client-side as well.

More context: [Dynamic default Actor run memory notion
spec](https://www.notion.so/apify/Dynamic-default-Actor-memory-WIP-293f39950a2280b9aa34fa9cd07f52a4?source=copy_link)

Author: danpoletaev

package-lock.json

@@ -0,0 +1,55 @@
+{
+    "name": "@apify/actor-memory-expression",
+    "version": "0.0.1",
+    "description": "Utility to evaluate dynamic memory expressions for Apify actors.",
+    "main": "./dist/cjs/index.cjs",
+    "module": "./dist/esm/index.mjs",
+    "typings": "./dist/cjs/index.d.ts",
+    "exports": {
+        ".": {
+            "import": {
+                "types": "./dist/esm/index.d.mts",
+                "default": "./dist/esm/index.mjs"
+            },
+            "require": {
+                "types": "./dist/cjs/index.d.ts",
+                "default": "./dist/cjs/index.cjs"
+            }
+        }
+    },
+    "keywords": [
+        "apify"
+    ],
+    "author": {
+        "name": "Apify",
+        "email": "[email protected]",
+        "url": "https://apify.com"
+    },
+    "contributors": [
+        "Jan Curn <[email protected]>",
+        "Marek Trunkát <[email protected]>"
+    ],
+    "license": "Apache-2.0",
+    "repository": {
+        "type": "git",
+        "url": "git+https://github.com/apify/apify-shared-js"
+    },
+    "bugs": {
+        "url": "https://github.com/apify/apify-shared-js/issues"
+    },
+    "homepage": "https://apify.com",
+    "scripts": {
+        "build": "npm run clean && npm run compile && npm run copy",
+        "clean": "rimraf ./dist",
+        "compile": "tsup",
+        "copy": "ts-node -T ../../scripts/copy.ts"
+    },
+    "publishConfig": {
+        "access": "public"
+    },
+    "dependencies": {
+        "@apify/consts": "^2.47.0",
+        "@apify/log": "^2.5.26",
+        "mathjs": "^15.1.0"
+    }
+}

packages/actor-memory-expression/CHANGELOG.md

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+export * from './memory_calculator';