0.29.0

• Breaking: Metadata::build_time() now returns
  Result<SystemTime, MaxMindDbError> instead of panicking on
  unrepresentable timestamps, and databases whose build_epoch cannot be
  represented as SystemTime are rejected as invalid during open and verify.
• Breaking: Reader::metadata is now private. Use Reader::metadata() to
  access validated metadata by shared reference.
• Breaking: Opening a database now rejects unsupported major format versions,
  unsupported IP versions, and zero-node search trees. Minor format versions
  are still accepted for forward compatibility.
• Fixed: within() and networks() now handle IPv6 databases without an
  IPv4 subtree without reading terminal data nodes as tree nodes or
  panicking while formatting low IPv6 networks.
• Fixed: Skipping ignored or unknown fields now enforces data-section
  bounds and the maximum nesting depth instead of accepting truncated
  values or overflowing the stack on deeply nested corrupt data.
• Internal: Added focused benchmarks for network iteration and serde
  unknown-field skipping, plus metadata build-time conversion, to guard
  performance-sensitive fixes.
• Documentation: Fixed intra-doc links so docs build with warnings denied,
  and added a CI check to keep them passing.