[wasphin]

What problem does this PR solve?

Problem Summary:

A Redis transaction can retain argument views across separate reads. The
connection currently clears its argument arena at the end of a read even
when a transaction handler is still active, so later reads can overwrite
those arguments before the transaction executes.

What is changed and the side effects?

Changed:

• Retain the argument arena while a transaction handler is active.
• Document the argument-string lifetime during a transaction.
• Add a real connection regression with separate requests and repeated
  transactions that retain argument views.

Side effects:

• Performance effects: Argument storage is retained until the transaction
  completes; its memory use depends on the accumulated transaction data.
• Breaking backward compatibility: No API signature changes.

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Check List:

• Changes compile locally.
• Added focused regression coverage.
• Please follow Contributor Covenant Code of Conduct.