🐛Prototype Pollution in @cloudflare__json-schema-walker

**Describe the bug**
The @cloudflare__json-schema-walker package contains prototype pollution vulnerabilities in the schemaWalk and subschemaWalk functions. Attacker-controlled input passed as the options parameter to these functions can modify Object.prototype via __proto__ keys (due to unsafe Object.assign operations), leading to potential unintended behavior, property injection, or breakage of dependent code.
**To Reproduce**
Steps to reproduce the behavior:
1. Install the vulnerable version of @cloudflare__json-schema-walker (version not specified in the report, assume latest affected).
2. Create a test script that imports the package and calls the affected functions with a malicious options object containing a __proto__ key:
```javascript
const schemaWalker = require('@cloudflare/json-schema-walker');
// Reproduce TP0001 (schemaWalk)
schemaWalker.schemaWalk({}, () => {}, {"__proto__": {"polluted": true}}, {});
// Reproduce TP0002 (subschemaWalk)
schemaWalker.subschemaWalk({}, '/test', () => {}, {"__proto__": {"polluted": true}}, {});
```
3. Run the test script (e.g., node test.js).
4. Check if Object.prototype.polluted is set to true (confirm prototype pollution).
If it's an issue with Cloudflare Tunnel:
4. Tunnel ID :
5. cloudflared config:

**Expected behavior**
The schemaWalk and subschemaWalk functions should sanitize or block __proto__ keys in the input options parameter to prevent modification of Object.prototype. Unsafe merging of user input into internal configuration objects should be avoided, and prototype pollution attempts should be mitigated (e.g., by stripping __proto__ keys, using safe object merging utilities, or validating input).
**Environment and versions**
OS: [Ubuntu 22.04]
Architecture: [e.g. ARM64]
Version: @cloudflare__json-schema-walker
Node.js Version: [e.g. 18.17.1, 20.9.0]
**Logs and errors**
For TP0001 (schemaWalk)
```text
[CASE_ID=TP0001] [VULN_GLOBAL] ERROR: postFunc is not a function
```
For TP0002 (subschemaWalk)
```text
[CASE_ID=TP0002] [VULN_GLOBAL] SAFE
```