chore: Bump DuckDB to v1.5.5

[jrosskopf]

Summary

• Bump the vendored DuckDB submodule from v1.5.3 to v1.5.5 (DUCKDB_EXPLICIT_VERSION, docs, and the MSVC-runtime comment reference updated alongside)
• Fix a leak in the DuckDBResult RAII wrapper: duckdb_query populates the result struct even on failure and it must always be passed to duckdb_destroy_result; v1.5.5's richer ErrorData on the error path made ASAN flag this in DuckDBResult RAII_test
• All runtime-autoloaded extensions verified available for v1.5.5: core repo (httpfs, ducklake, fts, json, postgres, sqlite, parquet), community bigquery, and erpl from get.erpl.io

Test plan

• make debug builds cleanly against v1.5.5 (no internal-API breakage in embed-fs / vfs_adapter / credential_manager)
• Full C++ unit suite: 644/645 pass; the one failure was the pre-existing RAII leak, fixed here (44 DuckDB-related tests re-run green after the fix)
• Server startup with examples/flapi.yaml: logs DuckDB 1.5.5, extensions autoload without warnings, authenticated GET /customers/ returns data
• CI matrix (Linux amd64/arm64, macOS, Windows) — note ccache is cold for this PR, expect long builds

Note for local dev: a stale ~/.duckdb/extensions/v1.5.5 cache with erpl sub-extensions extracted by an older build causes a metadata-mismatch crash at startup — delete ~/.duckdb/extensions/v1.5.5/linux_amd64/erpl* and let it re-install.

🤖 Generated with Claude Code

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