feat(DBI): driver-architecture + pure-Perl DBD support

[fglock]

Summary

Previously use DBI; DBI->install_driver("NullP") died with Undefined subroutine &DBI::install_driver. The bundled DBI.pm talked to the Java DBI backend only, bypassing the DBI driver architecture (DBD::<name>::driver factories, DBI::_new_drh / _new_dbh / _new_sth, DBD::_::common / dr / db / st base classes). That path covers JDBC drivers (SQLite, H2, ...) but not the pure-Perl DBDs bundled with upstream DBI — DBD::NullP, DBD::ExampleP, DBD::Sponge, DBD::Mem, DBD::File, DBD::DBM — which the DBI self-tests rely on extensively.

This PR adds the minimum driver-architecture pieces needed by those DBDs, in a new file src/main/perl/lib/DBI/_Handles.pm:

• DBI->install_driver / installed_drivers / data_sources / available_drivers / setup_driver;
• DBI::_new_drh / _new_dbh / _new_sth (handle factories, returning plain blessed hashrefs — no tie magic);
• DBI::_get_imp_data (stub);
• DBD::_::common / dr / db / st base classes with FETCH, STORE, err, errstr, state, set_err, trace, trace_msg, parse_trace_flag(s), func, dump_handle, visit_child_handles, default connect / connect_cached, quote, quote_identifier, data_sources, disconnect, commit, rollback, ping, finish, fetchrow_array, fetchrow_hashref, rows, bind_col(s), bind_param(_array), execute_array, _set_fbav;
• Stub DBI::dr / DBI::db / DBI::st packages so isa('DBI::dr') succeeds; DBD::_::<suffix> inherits from DBI::<suffix>.

DBI.pm's connect wrapper now detects a pure-Perl DBD (has driver() but no _dsn_to_jdbc) and routes through install_driver($name)->connect(...) instead of the JDBC backend.

Lives in a separate .pm for the same per-method bytecode-size reason as DBI/_Utils.pm from #540.

Effect on jcpan -t DBI (stacked on #542)

	Files	Subtests	Passing	Failing
before	200	946	676	270
after	200	1600	1240	360

+564 subtests now pass, +654 more are reached. 10 fewer test files fail overall. The remaining failures are real DBI-level issues (DBI::PurePerl, DBD::File / DBM / Gofer, a handful of handle-tracking edge cases) tracked as Phase 3 in dev/modules/dbi_test_parity.md.

Depends on

• fix(backend): interpreter fallback on runtime VerifyError #542 (interpreter fallback on runtime VerifyError) — needed so many of the test files get past their BEGIN blocks at all. This PR is based off that branch.

Test plan

• make (full unit tests) passes.
• ./jperl -e 'use DBI; my $drh = DBI->install_driver("NullP"); my $dbh = DBI->connect("dbi:NullP:", "", ""); my $sth = $dbh->prepare("SELECT 1"); $sth->execute' now works.
• ./jperl ~/.cpan/build/DBI-1.647-5/t/02dbidrv.t runs 37+ subtests (previously: died on line 155 with Can't locate object method install_driver).
• jcpan -t DBI baseline matches the table above.

Generated with Devin

[fglock]

Superseded by unified PR (see new PR). All four commits rebased into a single branch targeting master.