chore(papi): commit the sources behind the four polkadot-api packages (#15)

* chore(papi): commit the sources behind the four polkadot-api packages

papi-utils, bizinikiwi-bindings, metadata-builders and merkleize-metadata
held only dist/ builds, and no repository held their source. Every
source map in dist/ embeds the TypeScript it was compiled from; that is
now committed as src/ (59 files), and it matches upstream polkadot-api
(MIT) exactly once @polkadot-api/* imports are renamed:

  papi-utils           @polkadot-api/utils 0.2.0
  bizinikiwi-bindings  @polkadot-api/substrate-bindings 0.16.6
  metadata-builders    @polkadot-api/metadata-builders 0.13.0-0.13.2
  merkleize-metadata   @polkadot-api/merkleize-metadata 1.1.21-1.1.23

scripts/check-papi-sources.mjs, run in the lint job, fails unless the
source embedded in dist/ is exactly the committed src/. tsconfig.json
excludes these src/ trees; ESLint already skipped the packages. Each
README now states the upstream package and version.

* chore(papi): keep the upstream sources in upstream-src/

The pezkuwi-dev build treats any package with a src/ directory as its
own: it requires our license header on every file and builds it. These
are upstream files that must stay byte-identical to the source embedded
in dist/, so they live in upstream-src/ instead, which neither the build
nor the root tsconfig picks up.

packages/papi-utils/upstream-src/mergeUint8.ts

@@ -0,0 +1,25 @@
+// TODO: deprecate spread overload in papi v2
+
+interface MergeUint8 {
+  /**
+   * @deprecated This overload will be removed in PAPI v2. Migrate as
+   *             follows:
+   *             mergeUint8(arr1, arr2) => mergeUint8([arr1, arr2])
+   */
+  (...inputs: Array<Uint8Array>): Uint8Array
+  (inputs: Array<Uint8Array>): Uint8Array
+}
+
+export const mergeUint8: MergeUint8 = (...i) => {
+  const inputs = (Array.isArray(i[0]) ? i[0] : i) as Uint8Array[]
+  const totalLen = inputs.reduce((acc, a) => acc + a.byteLength, 0)
+  const result = new Uint8Array(totalLen)
+
+  for (let idx = 0, at = 0; idx < inputs.length; idx++) {
+    const current = inputs[idx]
+    result.set(current, at)
+    at += current.byteLength
+  }
+
+  return result
+}