Support auto adding of pure for known patterns.

### 🆒 Your use case

There are common patterns of `Symbol()` / `Symbol.for()`/ `new Proxy()` that could be auto annotated with this plugin (otherwise won't be tree-shaken, it is so common in some libs)

### 🆕 The solution you'd like

Other than `functions: {}` allow a flag or do it by default

### 🔍 Alternatives you've considered

_No response_

### ℹ️ Additional info

_No response_

Review the plugin's existing functions configuration and pure-annotation behavior, then determine how the requested Symbol(), Symbol.for(), and new Proxy() patterns should be recognized or configured. Done means the supported patterns are documented, annotated correctly for Rollup tree-shaking, and covered by tests.

Written by the indexing model from the issue text.