feat(js): add sticky assignment support with remote resolver fallback

[nicklasl]

Summary

Adds sticky assignment support to the JavaScript OpenFeature provider using remote resolver fallback.

How it works

• Local WASM resolver attempts to resolve flags first
• If sticky assignment data is needed, falls back to Confidence cloud resolvers
• Materializations stored on Confidence servers with 90-day TTL (auto-renewed)
• Zero configuration required - works out of the box

Key changes

• Implemented ResolveWithStickyRequest support in provider
• Added remote resolver fallback for missing materializations
• Updated README with sticky assignments documentation
• Added comprehensive tests for sticky resolve behavior

Future work

Custom MaterializationRepository support is planned for a future release to allow users to provide their own storage backend (Redis, database, file system, etc.). The interface and utilities are already in place but marked as WIP.

🤖 Generated with Claude Code

[andreas-karlsson]

It should be possible to load for multiple units?

[andreas-karlsson]

Same, should be possible to store multiple units?

[andreas-karlsson]

We should think a bit about this interface. Is it only us who should implement it? Do we need it to specify the full model of data? Could it for instance be a simple KV store with bytebuffer values? Probably not, since we actually update the values rather than overwriting them. It could be a flattened key space though like type Record = [key:[unit:string, materialization:string, rule:string], variant:string]. Don't feel confident we should use the PB generated types in the interface anyhow.

[andreas-karlsson]

In general, do we expect the implementation to be super low latency and we can afford to load materializations one by one, or does it need to support loading in bulk?

[andreas-karlsson]

Here is an API proposal:

type Variant = string;
type MaterializationInfo = {
  [unit:string]: {
    [materialization:string]: {
      [rule:string]: Variant
    }
  }
}
type RuleList = string[]
type MaterializationQuery = {
  [unit:string]: {
    [materialization:string]: RuleList
  }
}

interface MaterializationRepository {

  loadMaterializations(query:MaterializationQuery):Promise<MaterializationInfo>
  storeMaterializations(materializations:MaterializationInfo):Promise<void>
}