bump: dbt Core to 1.12

[chenzl25]

Summary

• release dbt-risingwave 1.12.0 with dbt-core 1.12 and dbt-postgres 1.11
• require Python 3.10+, matching dbt-core 1.12, and refresh the tox/CI version matrix
• synchronize the copied PostgreSQL connection opener with upstream autocommit and record/replay behavior while preserving RisingWave's gssencmode=disable
• pin development tests to released dbt packages instead of upstream main branches, and remove obsolete test/tool dependencies that no longer install cleanly

The experimental v2 parser remains opt-in; this PR does not change parser defaults.

Validation

• uvx tox -r -p auto -e py310,py311,py312,py313 — 34 tests passed on each Python version
• all 14 projects under tests/e2e passed dbt parse --no-partial-parse with dbt-core 1.12.2
• python -m pip check
• wheel and sdist build followed by twine check
• YAML, Black, Flake8, whitespace, and git diff --check

The existing GitHub workflow will exercise the adapter against live RisingWave instances.

Upstream references:

• https://github.com/dbt-labs/dbt-core/releases/tag/v1.12.2
• https://docs.getdbt.com/docs/dbt-versions/core-upgrade/upgrading-to-v1.12