[Feature] Introduce a common Table hierarchy for managed, format and system tables #526

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I searched existing issues. #459 tracks the broader, multi-step table refactoring; this issue covers the common table hierarchy step following the merged FileStore factory extraction in #516.

Motivation

Table-kind dispatch and operator assembly are concentrated in table.cpp, while format tables have a separate handle and system tables are not represented consistently through Catalog::GetTable(). The existing Table::NewScan/NewRead/NewWrite/NewCommit methods delegate to context-based factories, so a loaded table's schema and storage identity do not determine the resulting operator.

Introduce a common table hierarchy, following Java Paimon's separation between managed, format and system tables, so catalogs return the appropriate table implementation and loaded tables create operators from their bound state.

Solution

• Make Table an abstract interface and implement it with FileStoreTable, FormatTable and SystemTable.
• Split managed-table behavior into append-only and primary-key implementations, reusing the FileStore factories already merged into main.
• Have filesystem and REST catalogs dispatch to the correct table type. System tables expose their own schemas and reject writes and commits.
• Make static operator factories load a table and delegate to its virtual operator methods. Loaded-table operations retain their schema, path and filesystem, apply operation options, and validate conflicting managed-table branches and types.
• Rename LatestSchema() to GetSchema() to describe the already-loaded schema without implying metadata refresh, and add regression coverage for the two operator entrypoints.

Anything else?

Part of #459 and a follow-up to #516. This issue is limited to the hierarchy step; execution-context separation and general table-copy/time-travel APIs remain separate follow-ups.

Public API changes are expected. Storage formats and protocols remain unchanged.

Are you willing to submit a PR?

• I'm willing to submit a PR!