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/hex.ts

@@ -0,0 +1,57 @@
+// https://jsben.ch/uWZw3
+const HEX_STR = "0123456789abcdef"
+export function toHex(bytes: Uint8Array): string {
+  const result = new Array<string>(bytes.length + 1)
+
+  result[0] = "0x"
+
+  for (let i = 0; i < bytes.length; ) {
+    const b = bytes[i++]
+    result[i] = HEX_STR[b >> 4] + HEX_STR[b & 15]
+  }
+
+  return result.join("")
+}
+
+// https://jsben.ch/URe1X
+const HEX_MAP: Record<string, number> = {
+  0: 0,
+  1: 1,
+  2: 2,
+  3: 3,
+  4: 4,
+  5: 5,
+  6: 6,
+  7: 7,
+  8: 8,
+  9: 9,
+  a: 10,
+  b: 11,
+  c: 12,
+  d: 13,
+  e: 14,
+  f: 15,
+  A: 10,
+  B: 11,
+  C: 12,
+  D: 13,
+  E: 14,
+  F: 15,
+}
+export function fromHex(hexString: string): Uint8Array {
+  const isOdd = hexString.length % 2
+  const base = (hexString[1] === "x" ? 2 : 0) + isOdd
+  const nBytes = (hexString.length - base) / 2 + isOdd
+  const bytes = new Uint8Array(nBytes)
+
+  if (isOdd) bytes[0] = 0 | HEX_MAP[hexString[2]]
+
+  for (let i = 0; i < nBytes; ) {
+    const idx = base + i * 2
+    const a = HEX_MAP[hexString[idx]]
+    const b = HEX_MAP[hexString[idx + 1]]
+    bytes[isOdd + i++] = (a << 4) | b
+  }
+
+  return bytes
+}