fix(cli): make --schema walk DataFusion catalogs (#92) (#95)

* fix(cli): make `--schema` walk DataFusion catalogs (#92)

`skardi query --schema` only iterated `data_sources[].name`, so a
catalog-mode source like the llm_wiki SQLite db (`hierarchy_level:
catalog`) reported its catalog name as a missing table while its real
tables (e.g. `wiki.main.wiki_pages`) stayed invisible.

Now walk `catalog_names() → schema_names() → table_names()` and
read each provider's schema directly. `-t TABLE` accepts a bare name
that resolves uniquely or a fully-qualified `catalog.schema.table`,
and ambiguous bare names error with the qualified candidates.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* fix(cli): address review feedback on `--schema` catalog walker

- Read default catalog/schema from `SessionConfig` via a new
  `CatalogDefaults` helper instead of hard-coding `datafusion`/`public`,
  so bare-vs-qualified rendering follows the session config.
- Skip `information_schema` and `pg_catalog` schemas in
  `enumerate_tables` so `--schema --all` stays focused on
  user-registered tables even if info-schema is enabled upstream.
- Reject partial/over-qualified `-t` filters (e.g. `a.b`, `a.b.c.d`)
  with a clear hint rather than silently falling through to a
  confusing "not found".
- Hoist test `use` statements to the top of `mod tests` and extract a
  shared `make_int_provider` helper.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: BtXin