feat: add system table framework with options table

[suxiaogang223]

Related to #141.

Summary

• Add Java-aligned system table identifier parsing for table$system_table and reserved branch form table$branch_xxx$system_table
• Add a lightweight system table framework with loader, scan, read, schema, and in-memory split support
• Implement the first metadata system table: table$options
• Route catalog schema/existence and scan/read paths through the system table framework
• Keep system table DDL unsupported

Tests

• Added identifier parsing tests for normal tables, system tables, branch tables, and invalid $ combinations
• Added catalog tests for table$options existence/schema and system table DDL rejection
• Added scan/read integration coverage for reading table$options
• Verified on Fedora:
  • cmake --build build-codex-system-table-pr1 --target paimon-core-test -j$(nproc)
  • ./build-codex-system-table-pr1/release/paimon-core-test --gtest_filter="IdentifierTest.*:FileSystemCatalogTest.TestOptionsSystemTableCatalog:TableReadTest.TestReadOptionsSystemTable"
• Ran formatting checks:
  • clang-format
  • cmake-format
  • pre-commit clang-format
  • pre-commit cmake-format

[suxiaogang223]

@lxy-9602 Hi, could you please help review this PR when you have time? This is the first step for system table support, adding the shared framework and the minimal table$options implementation. I’d like to continue with the follow-up system table work after this direction is reviewed. Thanks!🤓

[lxy-9602]

Thanks for this great contribution — the code is clean, well-structured, and clearly reflects the effort you've made to bridge C++ and Java differences.

Looking forward to your follow-up updates and more system table support!