refactor(tuple): return TupleEntry from iterators

[tisonkun]

Summary

• restore TupleEntry as a public re-export and return borrowed named entries from mutable, compact, and view iterators
• keep Tuple iteration zero-copy while aligning access through entry.hash() and entry.summary()
• migrate documentation and integration tests, and update the unreleased changelog

Testing

• cargo x check
• cargo x test
• cargo x lint