Interop fixtures

Real files from other wallets, kept so that nullroute's coordinator import (packages/core/src/descriptor/coordinator.ts, spec core.descriptor.coordinator) is tested against what those programs actually write rather than against files its own tests made up.

Nothing here is edited. Every file is either a verbatim copy of a file another project keeps as a test fixture, or the output of a real Bitcoin Core run that anyone can repeat. Each file's SHA-256 is in SHA256SUMS, which sha256sum -c reads, and the hash of SHA256SUMS itself is pinned in packages/core/src/descriptor/coordinator.spec.yaml, so make verify fails if any of it changes without the spec changing too.

cd spec/interop && sha256sum -c SHA256SUMS

The tests are in packages/core/test/interop.fixtures.test.ts and bind to INV-COORD-1 to INV-COORD-6. Every expected value in them comes from somewhere other than nullroute's code: a value Sparrow's own test asserts for that file, an address BIP-129, BIP-84 or BIP-86 publishes, or what Bitcoin Core derived.