Remove Connection#select after migrating spec call sites off the internal helper

[yahonda]

Background

OracleEnhanced::OCIConnection#select and OracleEnhanced::JDBCConnection#select have no callers inside the library (grep against lib/ returns zero hits). PR #2768 marks both :nodoc: because they remain spec-only helpers. The deprecation_warning that PR #2768 briefly added is dropped in the same PR — the retry behaviour that vanished with the driver-level with_retry removal only fired under auto_retry = true, which already raises NotImplementedError through OracleEnhancedAdapter#auto_retry=, so there are no real users to warn.

This issue tracks the removal step on its own, so the spec migration scope stays separate from #2768.

Goal

Delete Connection#select (and the Connection#select_no_retry companion on JDBC) once spec call sites have been migrated to an alternative. Driver-level query helpers that bypass the AR adapter add internal-API surface that does not pull its weight (only specs use it, and only for admin / V$ queries that the AR adapter can serve too).

Steps

1. Catalog the remaining call sites in spec/active_record/connection_adapters/oracle_enhanced/connection_spec.rb:
   • should execute SQL select (@conn.select("SELECT * FROM dual")) and should execute SQL select and return also columns — these are literal regression tests for the helper. Delete or rewrite to assert the equivalent AR-API behaviour.
   • kill_current_session helper — @conn.select(...) for userenv('sessionid') lookup. @sys_conn.select(...) for the v$session lookup. The latter needs SYS privileges, so it cannot trivially move to ActiveRecord::Base.lease_connection (which is the application user).
   • connection_id_from_server helper — same @sys_conn.select(...) SYS-only lookup.
2. For the @conn.select(...) lookups, replace with ActiveRecord::Base.lease_connection.select_one(...) (or select_all(...).to_a.first).
3. For the @sys_conn.select(...) SYS-only lookups, pick one of:
   • Replace with @sys_conn.exec(...) + manual cursor iteration (cursor.fetch; cursor[col_index]; cursor.close).
   • Add a small spec helper module that wraps the cursor iteration so the call sites stay readable.
   • Establish a separate AR connection pool for the SYS user and route the SYS lookup through lease_connection.select_one on that pool.
4. Once all call sites are gone, remove Connection#select from both oci_connection.rb and jdbc_connection.rb, and remove Connection#select_no_retry from jdbc_connection.rb (it has no other callers).

Out of scope

Connection#exec is not part of this cleanup. It is reached widely from lib/ (DDL, prepared statements, schema introspection) and is part of how the adapter actually talks to OCI / JDBC.

[yahonda]

Adjacent cleanup surfaced by PR #2768 review: the _no_retry suffix on exec_no_retry and select_no_retry in jdbc_connection.rb is now misleading. There is no _retry counterpart anywhere — the driver-level with_retry was deleted in #2768, so the "no retry" qualifier no longer distinguishes anything.

• select_no_retry only has Connection#select as a caller and goes away together with it (step 4 above already covers this).
• exec_no_retry is still reached from two places: ping (exec_no_retry("select 1 from dual")) and Connection#exec (the public entry point that now just delegates to it). Rename to something neutral (e.g. fold its body into Connection#exec directly, or rename to _execute_statement / _run_statement) as part of this issue's cleanup so the JDBC code does not keep a misleading _no_retry name post-removal.

[yahonda]

Deferring until a later release cycle. Recent PRs (#2768, #2773 via #2775, #2776) already moved a lot of internals in quick succession, and Connection#select is :nodoc: so leaving it in place for now costs nothing user-visible. Re-evaluate once the rest of the migration has had time to settle.