feat: expose roots from zerokit

[weboko]

Problem

@waku/rln maintains its roots here by essentially relying on zerokit to give it current root here.

These roots lately are used to verify a proof - which is done again inside of zerokit here.

Solution

Expose from wasm following API:

• getRoots - gives requested amount of latest roots (default to 5);
• remove a need to pass roots to verify as they are already inside of zerokit;

getRoots still can be exposed as might be used later or by a consumer.

[weboko]

Ice boxing for now. Re-prioritizing after approach to RLN is clear in light clients.