crypto: 100,000 iterations of PBKDF2 is insecure

Hello,

`workerd` (and Cloudflare Workers) limits the number of `PBKDF2` iterations to 100,000 to avoid DoS.

We can see the code here: https://github.com/cloudflare/workerd/blob/d1a3c89716591753406923e177b54da3475dd01c/src/workerd/api/crypto-impl-pbkdf2.c%2B%2B#L45C31-L45C37

While I understand the reason, especially in a multi-tenant environment like Cloudflare Workers, 100,000 iterations is far from secure, as per [OWASP guidelines](https://cheatsheetseries.owasp.org/cheatsheets/Password_Storage_Cheat_Sheet.html), which, in 2023, recommends at least 210,000 iterations for `PBKDF2-SHA-512` and 600,000 iterations for `PBKDF2-SHA-256`, making any application hashing passwords from Cloudflare Workers insecure.

This is why I'm requesting an increase to at least 400,000 iterations.