Introduce a generic pubsub mod in cdk-common (#1098)

* pubsub: consolidate into Spec, adopt Arc<SubscriptionId>, and wire through  wallet/mint/WS/FFI

Refactor the pub/sub engine to a single Spec trait, move Event alongside it,
and propagate Arc-backed subscription IDs across the stack. This simplifies
generics, clarifies responsibilities, and preserves coalescing +
latest-on-subscribe semantics.

-   **Single source of truth:** `Spec` owns `Topic`, `Event`, `SubscriptionId`,
    `Context`, new_instance, and fetch_events.
-   **Lean & explicit API:** Remove Topic trait split;
    `Subscriber::send(Event)` carries sub-ID internally.
-   **Performance/ergonomics:** `Arc<SubscriptionId>` avoids heavy clones and
    makes channel/task hops trivial.

-   Introduce `pub_sub/typ.rs` with:
    -   trait `Spec`
    -   trait `Event` colocated with Spec.
-   Remove `pub_sub/event.rs` fold `Event` into `typ.rs`.
-   Make `Pubsub<S>` generic over `Spec` and store `Arc<S>`.
-   The subscriber holds `Arc<SubscriptionId>` and deduplicates the latest
    entry per subscription.
-   SubscriptionRequest: rename SubscriptionName → SubscriptionId; return
    `Arc<...>` from `subscription_name()`.
-   Remote consumer (Transport) now parameterized by `Spec`; control types
    updated:
    -   `StreamCtrl<S>`, `SubscribeMessage<S>`, internal caches keyed by
        `S::Topic`.
-   Mint/wallet:
    -   Mint: `MintPubSubSpec` (Context = `DynMintDatabase`),
        `PubSubManager(Pubsub<MintPubSubSpec>)`.
    -   Wallet: lightweight MintSubTopics Spec with `Context = ()`.
-   IDs go Arc end-to-end:
    -   cdk-axum WS maps `HashMap<Arc<SubId>, JoinHandle<()>>`, publisher sends
        `(Arc<SubId>, NotificationPayload)`.
    -   `subscription::{Params, WalletParams}` now use `Arc<...>`.
    -   cdk-ffi conversions & wallet glue updated.
    -   Integration tests updated for new types.

-   Coalescing unchanged: multiple local subs to the same topic are combined
    into a single remote sub.
-   Backfill via `Spec::fetch_events(topics, Subscriber)`; Subscriber enforces
    latest-only dedupe per subscription.

**Result:** a slimmer, more maintainable pub/sub core that’s easier to embed
across mint, wallet, transports, and FFI without sacrificing performance or
semantics.


---------

Co-authored-by: thesimplekid <tsk@thesimplekid.com>

.github/workflows/ci.yml

@@ -490,6 +490,16 @@ jobs:
     steps:
       - name: checkout
         uses: actions/checkout@v4
+      - name: Free Disk Space (Ubuntu)
+        uses: jlumbroso/free-disk-space@main
+        with:
+          tool-cache: false
+          android: true
+          dotnet: true
+          haskell: true
+          large-packages: true
+          docker-images: true
+          swap-storage: true
       - name: Install Nix
         uses: DeterminateSystems/nix-installer-action@v17
       - name: Nix Cache