fix: reject Paimon reads and writes on iceberg/object/lance tables

[plusplusjiajia]

Purpose

Follow-up to #733: the default Catalog::load_table wrapped get_table's result as LoadedTable::Paimon unconditionally, so a catalog that does not override it skipped the resolver entirely. Beyond that, a table declared iceberg-table, object-table or lance-table could still be read or written as Paimon through several other paths; this PR closes them.

Brief change log

Catalog

• The default Catalog::load_table classifies from the loaded table's own options and goes through the checked LoadedTable::external constructor, so a catalog that only implements get_table fails closed
• The default list_partitions refuses external tables.

Core storage boundary

• CoreOptions::ensure_read_authorized — already called at every path that reads or mutates table storage — now also refuses an engine-served declared type; ensure_engine_can_serve keeps the auth-only half.
• IncrementalScan::plan, TableCommit::abort (type-only) and the shared write validator gain the missing check.

Runtime type immutability

• copy_with_options pins the stored type the way it pins query-auth.enabled.
• copy_with_branch and copy_with_time_travel refuse external tables before any IO.

DataFusion

• Guards kept only where core cannot cover: procedures (tag/branch managers), SHOW CREATE TABLE (no storage IO), and provider construction (validates before registering with the blob-reader registry).