Include tuple indexes in keypath discovery and matching

[xiehuanyi]

Indexed keypath discovery skips tuples, although direct indexed reads and flattening already support them. As a result, benedict({"items": ({"value": 1},)}).match("items[*].value") returns an empty list even though d["items[0].value"] returns 1.

Traverse tuples alongside lists when indexes are enabled. Add regressions for tuple mappings, nested tuples and lists, wildcard matching, and the indexes-disabled behavior.

Validation: both new regressions fail on unchanged main. The full unittest suite passes after the fix (928 tests, 1 skipped); Ruff lint/format and mypy (64 source files) pass.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.51%. Comparing base (8c3371f) to head (6637869).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #620   +/-   ##
=======================================
  Coverage   98.51%   98.51%           
=======================================
  Files          64       64           
  Lines        2430     2430           
=======================================
  Hits         2394     2394           
  Misses         36       36           

Flag	Coverage Δ
unittests	98.51% <100.00%> (ø)

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