feat: add global system tables framework under sys database

[suxiaogang223]

Summary

Add global system table support under the sys database, enabling catalog-level metadata queries.

Closes part of #141.

Changes

Infrastructure

• Add GetOptions() to Catalog interface for catalog-level config access
• FileSystemCatalog stores and exposes catalog options
• New GlobalSystemTableLoader with independent registry for sys tables
• Extend SystemTablePath with is_global flag and TryParsePath to detect sys/ paths
• FileSystemCatalog handles sys database in ListTables/DatabaseExists/TableExists/LoadTableSchema

Global System Tables

Table	Status	Columns
sys.catalog_options	✅ Complete	key, value
sys.all_table_options	✅ Complete	database_name, table_name, key, value
sys.tables	✅ Basic info ready	database_name, table_name, table_type, partitioned, primary_key, record_count; file stats columns (file_size_in_bytes, file_count, last_file_creation_time) return null
sys.partitions	🔶 Skeleton	Schema defined; returns empty result set

Files Changed

 include/paimon/catalog/catalog.h                   |   5 +
 src/paimon/CMakeLists.txt                          |   1 +
 src/paimon/core/catalog/catalog.cpp                |   2 +-
 src/paimon/core/catalog/file_system_catalog.cpp    |  39 ++-
 src/paimon/core/catalog/file_system_catalog.h      |   5 +-
 .../core/table/system/global_system_tables.cpp     | 370 +++++++++++++++++++++
 .../core/table/system/global_system_tables.h       | 117 +++++++
 src/paimon/core/table/system/system_table.cpp      |  28 +-
 src/paimon/core/table/system/system_table.h        |   2 +
 .../core/catalog/file_system_catalog_test.cpp      |  14 +-
 10 files changed, 573 insertions(+), 10 deletions(-)

Dependency on #309 (codex/system-table-files-manifests-pr4)

The ManifestFile / ManifestList reading infrastructure from #309 is needed to complete:

• sys.tables: populate file_size_in_bytes, file_count, last_file_creation_time by aggregating manifest entries from the latest snapshot
• sys.partitions: read manifest entries grouped by partition to output per-partition statistics

Once #309 lands, the remaining TODO items in global_system_tables.cpp can be resolved in a follow-up PR.

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