[bfrancojr]

A schema with (pxf.required) = true and (pxf.default) on one field now fails when it is bound, as draft -01 requires. Before, it bound here, and a document omitting the field got an error from this port even though the same schema could mean something else in another engine.

Fixes #50

Changes

• ValidateFile reports the pair as a new ViolationKind::kRequiredOption. The check sits with the other field checks, so it covers the import closure, and Unmarshal and UnmarshalFull refuse the schema.
• (pxf.required) = false beside a default stays accepted.
• This port reads only the bracket options. It has no @required / @default carrier reader, so there is one spelling to check.

Also fixed

• The bind-failure Status now starts PXF schema violations:, matching Go. It used to say reserved-name violations, which would be wrong for this rule and was already wrong for (pxf.key). Anything matching the old text needs updating.

Evidence

• ctest --test-dir build --output-on-failure: 100% tests passed out of 301, including the three new PxfSchema tests. No existing test schema carried the pair, so none needed changing.
• With the check removed from schema.cc, RequiredWithDefaultRejected and RequiredWithDefaultInImportReported fail (Which is: 0, wanted 2 and 1). RequiredFalseBesideDefaultAccepted passes either way, as it should.
• clang-format --dry-run -Werror is clean on the changed sources, using version 23, not the 18 that CI uses.

Not covered

BindRow and DatasetReader::Scan skip every bind-time check, so this rule does not reach them, like the reserved-name and (pxf.key) rules. A probe showed it, and #51 tracks it because the fix needs a design choice. scripts/cross_security_check.sh is not evidence here: it does not exercise this rule.