Use LOCAL_QUORUM and LOCAL_SERIAL as query defaults #1253

Problem

The default execution profile and legacy session use LOCAL_ONE for ordinary reads and writes. Their serial consistency is unset, so conditional writes omit the serial consistency field and use the protocol's SERIAL default.

This means an application using the driver's defaults does not get a local quorum for ordinary operations, and lightweight transactions span data centers during the serial phase. The existing DataStax Apollo-specific adjustment changes only the ordinary consistency default.

Expected behavior

Use LOCAL_QUORUM for ordinary operations and explicitly send LOCAL_SERIAL for the serial phase of lightweight transactions, through both execution profiles and legacy sessions. Simple, prepared, bound, and batch requests should inherit these defaults while preserving explicit application overrides, including an explicitly unset serial profile setting.

Document the compatibility change: a local quorum must be available, and the default LWT serial scope becomes the local data center. Applications that need the previous defaults can explicitly configure LOCAL_ONE and SERIAL, except on DataStax Apollo/Astra clusters. Those clusters already used LOCAL_QUORUM and need only an explicit SERIAL setting to retain their previous behavior.