Support for Recursive Descent (..) Operator

[ljluestc]

Description

This PR implements support for the recursive descent operator .. (deep scan) in JSONPath, addressing issue #42.

Changes

• Tokenization: Updated tokenize to correctly identify .. as a distinct token instead of converting it to *. Added deduplication to handle cases like .... gracefully.
• Parsing: Updated parse_token to recognize the .. token and return a new recursive operation.
• Execution: Implemented recursive logic in the Lookup function.
  • Added getAllDescendants helper to traverse the object graph (Maps, Slices, Arrays).
  • Added lookahead logic to filter out Slice containers from recursive results when the subsequent step is a key lookup. This prevents duplicate matches (one from the container, one from the elements).
• Testing:
  • Added TestRecursiveDescent covering $..author and $..price scenarios.
  • Updated existing tests in token_cases within jsonpath_test.go to match the new tokenization behavior (expecting .. instead of * for valid recursive queries).

Verification

• Added new test case TestRecursiveDescent passes.
• All existing tests pass.

Fixes #42