Reranker dynamic quantization

### Feature request

--dtype support for rerankers

### Motivation

Easily quantize cross encoder models

### Your contribution

. (will look into this)

The issue does not name any files, tests, or entry points. Start by locating the reranker and cross-encoder model handling, then trace how model dtype is selected and whether dynamic quantization is already supported elsewhere. Done means rerankers accept the requested dtype and quantized cross-encoder behavior is covered by tests.

Written by the indexing model from the issue text.