[belfordzjeeves]

Fixes #201

Root cause (two parts)

1. validateItem in src/index.ts only dispatched on schema.type; a schema carrying oneOf (and no type) silently validated as true at its own level.
2. Worse, the traverse(schema, ...) walk in validator() visited each branch at paths like $.oneOf[0], and schemaPathToRegularPath drops the oneOf[0] token, so every branch subschema was validated against the parent's data — producing false errors (e.g. the {type: "number"} branch checked against "potato").

Fix

• src/base-validators/oneOf.ts (new): OneOfValidationError following the existing error-class pattern; added to the ValidationError union in src/index.ts.
• validateItem now handles oneOf: it counts branches where validateItem(branch, data) === true. Exactly one match returns true; otherwise a OneOfValidationError is collected with reason expected data to match exactly one schema in oneOf, but N matched. Recursion through validateItem makes nested oneOf (in a branch, in an object property) work.
• The validator() traverse callback skips subschemas sitting under a oneOf keyword (matched by /(^|\.)oneOf\[\d+\]/), since validateItem handles them recursively at the oneOf schema. A data property literally named oneOf yields paths like $.properties.oneOf (no bracket index) and is deliberately not skipped — covered by a precision test.
• Out of scope: allOf/anyOf/not untouched.

Verification

• Issue repro before fix: both cases returned ValidationErrors; after fix both return true.
• Full suite: 7 suites, 45 tests, all green. Coverage: 98.39% statements / 94.5% branches / 100% functions / 98.3% lines — above the jest.config.js thresholds (94.28 / 87.77 / 100 / 93.99). New oneOf.ts is 100% covered.
• npx tsc --noEmit clean.
• New regression tests in src/index.test.ts: the issue's two cases verbatim, both-branches-match, neither-matches, oneOf in an object property (valid + invalid), oneOf nested in a oneOf branch, and the property-literally-named-oneOf precision test.