Parse an event that carries a key NIP-01 does not name

[sepehr-safari]

Closes #106.

fromJson and the relay message parser read the event object with default std.json options, so a key beyond the seven NIP-01 names failed the parse with UnknownField. A valid event carrying one was dropped, and on a relay connection it failed the whole EVENT message.

The id is the hash of the seven named fields and the signature is over the id, so an extra key cannot change what was signed. Both parse paths now share one set of options that skips unknown keys. Duplicate keys are still refused: with two content keys it would be ambiguous which one the signature covers.

Tests

an event carrying a field NIP-01 does not name still parses and verifies signs an event, adds an array-valued and a nested object-valued key, and checks that it parses, keeps its id, verifies, and writes back out byte-identical to what was signed. It failed with UnknownField before the change.

parse EVENT message whose event carries a field NIP-01 does not name covers the relay message path, which goes through fromValueLeaky rather than fromJson. It also failed before the change.

an event naming the same field twice is still refused pins the duplicate-key refusal so a later loosening of the options cannot drop it quietly.

All 206 tests pass.