docs(vrl): add documentation for IPCrypt functions

Add documentation for the new `encrypt_ip` and `decrypt_ip` VRL functions
that implement format-preserving encryption for IP addresses.

These functions support two modes:
- AES128: Scrambles entire IP address using AES-128 encryption
- PFX: Prefix-preserving mode that maintains network hierarchy

The functions implement the `ipcrypt-deterministic` and `ipcrypt-pfx`
algorithms from the IPCrypt specification.

Related PR: vectordotdev/vrl#1506

Author: alterstep

.github/actions/spelling/allow.txt

@@ -237,6 +237,7 @@ Intenso
 INTERLAKEN
 ionik
 ipallowlist
+ipcrypt
 ipod
 ircd
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