Axios: ReDoS (O(N²)) in shouldBypassProxy host normalization, reachable via untrusted redirect Location

## Summary Axios `shouldBypassProxy()` normalizes hostnames with `hostname.replace(/\.+$/, '')`. For a hostname shaped as many dots followed by a non-dot, the anchored regex can perform quadratic backtracking. Because axios re-evaluates proxy bypass rules for redirected requests, a malicious server can trigger this synchronous work through a crafted redirect `Location`. The issue affects Node.js applications that use environment proxy variables with `NO_PROXY` and allow redirects. ## Impact An attacker-controlled server can return a redirect whose hostname causes the axios process to spend significant CPU time in synchronous hostname normalization. During this time, the Node.js event loop is blocked and the application cannot handle other work on that thread. This is an availability-only issue. It does not disclose request data or modify requests. ## Affected Functionality Affected: - Node.js HTTP adapter. - Environment proxy handling through `HTTP_PROXY` or `HTTPS_PROXY`. - `NO_PROXY` or `no_proxy` set to a non-empty value. - Redirects followed by axios or `follow-redirects`. Not affected: - Browser adapters. - Requests with `proxy: false`. - Requests with no `NO_PROXY` value. - Requests with `maxRedirects: 0`, unless application code manually follows the malicious redirect and re-enters axios. ## Technical Details `lib/helpers/shouldBypassProxy.js` contains: ```js return unmapIPv4MappedIPv6(hostname.replace(/\.+$/, '')); ``` When the hostname is `"." * n + "a"`, the `$` anc