refactor: pattern rune

[harrysolovay]

Simplifies defining Capi Runes, as we no longer need to include the ctor (and it's somewhat intimidating signature).

Before

export class BlockRune<out C extends Chain, out U> extends Rune<known.SignedBlock, U> {
  constructor(
    _prime: BlockRune<C, U>["_prime"],
    readonly chain: ChainRune<C, U>,
    readonly hash: Rune<string, U>,
  ) {
    super(_prime)
  }
  // ...

After

export class BlockRune<out C extends Chain, out U>
  extends PatternRune<known.SignedBlock, C, U, Rune<string, U>>
{
  // ...

---

TODO: decide on name. PatternRune doesn't feel the most fitting.