SEP-1577: support Sampling With Tools

[findleyr]

Tracking issue: if SEP-1577 lands for the 2025-11-25 version of the spec, we must support it.

[findleyr]

This is somewhat straightforward (at least to do the basic thing: integrating with our existing tool APIs is more complicated).

However, it's yet another case where the client wants to customize capabilities. We need to figure out the pattern for doing so.

[findleyr]

This is not going to make it into the 1.2 release--moving to 1.3.

Better to get the 1.2 release out, and iterate, than hold it for this feature.