Support table prefixes in ActiveRecord adapter

[jnunemaker]

Summary

ActiveRecord users can namespace Flipper tables with table_prefix: without defining custom feature and gate model classes. The adapter creates internal subclasses that target the prefixed tables while preserving explicit feature_class and gate_class overrides.

Both flipper:active_record and flipper:update accept --table-prefix, so initial migrations and future schema updates generate matching table names, migration filenames, and migration classes without manual edits.

Validation

• ActiveRecord Minitest: 36 runs, 934 assertions, 0 failures
• Rails generator tests: 15 runs, 105 assertions, 0 failures
• ActiveRecord RSpec: 162 examples, 0 failures; 110 environment-dependent pending examples
• git diff --check

The broader Redis-backed Minitest suite was not run because it requires FLUSHDB against a local Redis instance.