fix: Oracle view crash caused by LONG column type in OracleNIO decoder

[datlechin]

Summary

Fixes #564 — clicking an Oracle view crashes TablePro with EXC_BREAKPOINT (SIGTRAP) in OracleNIO's OracleBackendMessageDecoder.decode.

Root cause: Oracle's data dictionary uses LONG data type columns. OracleNIO 1.0.0-rc.4 crashes with a fatal error (force unwrap/precondition failure) when decoding non-NULL LONG values. When fetchColumns queries ALL_TAB_COLUMNS.DATA_DEFAULT (LONG type), views have non-NULL values (column expressions) that trigger the crash. Tables usually have NULL defaults, so the decoder is never triggered — which is why only views crash.

Three fixes in OraclePlugin.swift:

• fetchColumns: Removed c.DATA_DEFAULT (LONG type) from the query to avoid triggering OracleNIO's broken LONG decoder. Default values show as nil.
• fetchViewDefinition: Replaced SELECT TEXT FROM ALL_VIEWS (TEXT is also LONG) with DBMS_METADATA.GET_DDL('VIEW', ...) which returns CLOB (safe).
• fetchTableMetadata: Added fallback query via ALL_TAB_COMMENTS when ALL_TABLES returns no rows (views are not in ALL_TABLES).

Test plan

• Connect to Oracle (gvenzl/oracle-free container)
• Click a view in the sidebar — should load data without crash
• Right-click view → Edit View Definition — should show DDL
• Verify table browsing still works (no regression)
• Check Structure tab for views shows comment metadata