test(reader): replace LayoutKindTest boolean matrix with a kind enum

[dfa1]

Follow-up to #93. The LayoutKindTest provider was a 5-boolean-per-row identity matrix:

Arguments.of(Layout.FLAT,    true, false, false, false, false),
Arguments.of(Layout.CHUNKED, false, true, false, false, false),
...

Every row encodes one fact — "exactly this kind's predicate is true." Replace the matrix with a Kind enum pairing each encoding id with its predicate, driven by @EnumSource:

for (Kind other : Kind.values()) {
    assertThat(other.predicate.test(sut))
            .as("%s on %s", other, kind.encodingId)
            .isEqualTo(other == kind);
}

other == kind states the intent directly. Same mutation coverage — each predicate is still asserted true for its own id and false for the others; the Layout kind mutants stay fully killed (reader still 5 survivors, all accepted/out-of-scope).

🤖 Generated with Claude Code