refactor: use generic constraints to fix @cloudflare/workers-types version conflicts

[imjlk]

Problem

Type mismatch errors occur when users have a different version of @cloudflare/workers-types than the library expects, particularly in monorepos or projects with multiple Cloudflare dependencies.

Solution

Introduced generic constraint interfaces (KVNamespaceConstraint, R2BucketConstraint) that define only the methods the library actually needs. Made withCloudflare and related types generic to accept any compatible KV/R2 types from user projects.

Before:

// Hard dependency on specific @cloudflare/workers-types version
import type { KVNamespace } from "@cloudflare/workers-types";
kv?: KVNamespace<string>;

After:

// Accepts any compatible type via generics
export interface KVNamespaceConstraint {
  get(key: string, options?: ...): Promise<string | null>;
  put(key: string, value: ..., options?: ...): Promise<void>;
  delete(key: string): Promise<void>;
}
kv?: TKV;  // Auto-inferred from user's types

Result

Users can now pass platform.env bindings directly without type errors. Types are automatically inferred:

withCloudflare({
  kv: platform.env.MY_KV  // ✅ Types inferred from your @cloudflare/workers-types
}, ...)

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/zpg6/better-auth-cloudflare@48

commit: baa382f