ci: split client library checks

[NikolayS]

Why

We support three client libraries, but CI currently reports them under one combined client-smoke job. That makes failures harder to triage and hides per-client status.

PR #84 had the right direction, but it is stale/conflicting. This is a clean current-main replacement with intentionally small scope.

What changes

Replaces client-smoke with separate jobs:

• Python client tests
• Go client tests
• TypeScript client tests

Each job gets its own fresh PostgreSQL 18 container, installs sql/pgque.sql, and sets PGQUE_TEST_DSN.

Suites run:

• Go: go test -race -v ./...
• Python: pytest -v clients/python/tests/
• TypeScript: Bun install/check + full vitest suite via bun run test

Also uses set -Eeuo pipefail in the new shell blocks and a Python venv to avoid PEP 668/system-pip issues.

Local validation

• YAML parses and has jobs: test, python-client-tests, go-client-tests, typescript-client-tests, verify
• Python job body passed locally against fresh PG18 before the final verbosity-only command tweak.
• TypeScript job body passed locally against fresh PG18 before removing smoke/benchmark extras.
• Go is not installed on this host, so exact go test -race is left to CI. Separate post-159 validation did run full Go tests against fresh PG18 successfully.