Bolt: emit native Path structures for query results

[robfrank]

Part of #4890. Epic #4882.

Covers conformance scenario TYPE-003 (bolt/conformance/spec.yaml), currently current_status: expected-fail.

Motivation

structure/BoltPath.java exists but has zero call sites constructing it anywhere in BoltStructureMapper - query results never actually produce native Bolt Path structures today. Drivers that expect a Path object from a path-returning query do not receive one.

Proposed design

• Detect path-typed results in BoltStructureMapper and construct BoltPath with the correct Bolt tag and the nodes/rels/indices field layout (unbound relationships + index sequence per the Bolt spec).
• Reuse the existing Node/Relationship/UnboundRelationship mappers for path element encoding.
• Ensure variable-length and fixed-length path results both serialize.

Acceptance criteria

• TYPE-003 passes across all five per-language suites (flip expected-fail -> passing in spec.yaml, remove the failure markers).
• A path-returning Cypher query yields a driver-side Path with correct nodes, relationships and ordering.
• No regression in Node/Relationship round-trips.

Dependencies

None. Writer-side only.

Effort estimate

S