[Feature] Bindings for the Workers Cache purge API (ctx.cache.purge)

[chrishiguto]

Is there an existing issue for this?

• I have searched the existing issues

Description

The runtime now exposes the newer per-Worker Workers Cache (announcement: https://blog.cloudflare.com/workers-cache/, docs: https://developers.cloudflare.com/workers/cache/), which is driven by Cache-Control / Cache-Tag response headers and has one imperative API: ctx.cache.purge() (also available as the cache export of cloudflare:workers). This is distinct from the Service-Worker Cache API already covered by worker::Cache (caches.default).

There's currently no way to call purge from Rust — worker::Context doesn't expose ctx.cache, and worker-sys has no binding for the CacheContext object. I'd like to add bindings for it.

Proposed API:

use worker::CachePurgeOptions;

// From the execution context (mirrors JS `ctx.cache`)
if let Some(cache) = ctx.cache() {
    let result = cache.purge(CachePurgeOptions::tags(["blog-posts"])).await?;
    if !result.success {
        console_error!("purge failed: {:?}", result.errors);
    }
}

// Or without a `ctx` in scope, via the `cloudflare:workers` export
let cache = worker::cache();
cache.purge(CachePurgeOptions::everything()).await?;

Shape of the types:

• Context::cache() -> Option<CacheContext> — None when the feature isn't enabled or the runtime predates it.
• worker::cache() -> CacheContext — the cloudflare:workers module export, for code with no ctx in scope.
• CachePurgeOptions with constructors tags(...), path_prefixes(...), and everything(), serialized to the runtime's camelCase keys (tags, pathPrefixes, purgeEverything). purge_everything is validated as mutually exclusive with the other two before crossing the FFI boundary.
• CachePurgeResult { success: bool, errors: Vec<CachePurgeError> } mirroring the runtime's result object; a rejected promise (e.g. permission error) surfaces as Err.