Axios: Prototype Pollution Gadget in axios toFormData Options

## Summary Axios form serialization reads `visitor`, `maxDepth`, `dots`, `indexes`, `metaTokens`, and `Blob` from an internal options object without own-property guards. When `Object.prototype` has been polluted elsewhere in the same process, those inherited values can change how axios serializes multipart and URL-encoded request bodies. Axios does not create the prototype pollution source. This is a read-side gadget: axios turns an existing same-process pollution condition into altered request serialization or request failures. ## Impact The impact depends on which property is polluted and which axios serialization path the application uses. Polluted `dots`, `indexes`, or `metaTokens` can change field names and cause the receiving service to parse different data than the caller intended. Polluted `maxDepth` can cause nested form submissions to throw `ERR_FORM_DATA_DEPTH_EXCEEDED`, producing request-level or service-level denial of service for affected workflows. Polluted `visitor` can execute as the serializer visitor if an attacker can place a function on `Object.prototype`, but that condition generally implies a stronger same-process code-execution or malicious-dependency primitive and should be described carefully. ## Affected Functionality Affected: - `axios.toFormData()`. - `transformRequest` paths that serialize plain objects to `multipart/form-data`. - URL-encoded form serialization paths that rely on the same helper. - `formSerializer` option defaults when the releva