nodejs: lazy per-backend libsimplex download (#7543)

* ci: drop dlltool from nodejs libs release

* nodejs: download libsimplex into the user cache

* nodejs: load libsimplex at runtime per backend

* support bot: select db backend with --db

* python: match backend switch error text

* nodejs: download prebuilt add-on at runtime

* ci: build nodejs add-on for libs release

* calculator bot: load libs and add-on in image

* support bot: document add-on override

* nodejs: keep worker test output free of colors

* nodejs: verify sha-256 of downloaded assets

* python: pin core libs release with sha-256

* ci: add packages release script

* ci: release nodejs add-on and open release PR

* ci: publish packages after release PR

* nodejs: keep npm from building the add-on

* calculator bot: build the add-on in the image

* ci: merge package release workflows

* ci: open release PR when publishing fails

* ci: build the add-on with node-addon-api only

* ci: skip publishing in a called packages workflow

* ci: update package release actions to Node 24

* nodejs: fix receive test timeout

* ci: test packages on pull requests

* nodejs: reuse the database in the close stress test

* ci: keep failed package tests from hanging

* ci: skip preset server tests

* ci: plan package builds from the changes

* ci: test packages with a given libsimplex

* ci: test packages with libsimplex of core changes

packages/simplex-chat-nodejs/src/api.ts

@@ -57,10 +57,8 @@ interface EventSubscriber<K extends CEvt.Tag> {
 }
 
 /**
- * Database configuration. The native library is built against exactly one
- * backend (see `simplex_backend` / `SIMPLEX_BACKEND` at install time); this
- * type makes the caller state which one they are targeting so field names
- * can't lie about their meaning.
+ * Database configuration. `type` selects the libsimplex backend loaded by
+ * `ChatApi.init`; one backend per process.
  */
 export type DbConfig =
   | {
@@ -108,7 +106,7 @@ export class ChatApi {
   private constructor(protected ctrl_: bigint | undefined) {}
 
   /**
-   * Initializes the ChatApi.
+   * Initializes the ChatApi, loading libsimplex for `db.type` (downloaded on first use).
    * @param {DbConfig} db - Database configuration (sqlite or postgres).
    * @param {core.MigrationConfirmation} [confirm=core.MigrationConfirmation.YesUp] - Migration confirmation mode.
    * @param {number} [queueSize] - Size of internal queues, the core default is used when omitted.
@@ -119,6 +117,7 @@ export class ChatApi {
     queueSize?: number
   ): Promise<ChatApi> {
     const [path, key] = dbConfigToMigrateArgs(db)
+    await core.loadLibrary(db.type)
     const ctrl = await core.chatMigrateInit(path, key, confirm, queueSize)
     return new ChatApi(ctrl)
   }