feat: add StringUtils, DateTimeUtils, PathUtil, OptionsUtils, RapidJsonUtil, and Jsonizable utilities

[dalingmeng]

Purpose

No Linked issue.

Introduce string/JSON/path utility modules to the apache/paimon-cpp codebase. These modules provide common string manipulation, date-time parsing, path operations, configuration option parsing, and JSON serialization helpers.

Introduce DateTimeUtils for timestamp parsing and formatting (date_time_utils.h)
Introduce TimezoneGuard test utility for timezone-dependent tests (timezone_guard.h)
Introduce StringUtils for string splitting, trimming, type conversion, and formatting (string_utils.h, string_utils.cpp)
Introduce RapidJsonUtil for JSON document read/write helpers (rapidjson_util.h)
Introduce PathUtil for file path manipulation and generation (path_util.h, path_util.cpp)
Introduce OptionsUtils for parsing configuration key-value options (options_utils.h)
Introduce Jsonizable CRTP base for JSON serialization/deserialization (jsonizable.h)

Tests

date_time_utils_test.cpp — Timestamp parsing, formatting, timezone handling
string_utils_test.cpp — String split, trim, conversion, and format operations
rapidjson_util_test.cpp — JSON document creation, read, and write
path_util_test.cpp — Path join, normalize, and UUID-based temp path generation
options_utils_test.cpp — Configuration option key-value parsing
jsonizable_test.cpp — JSON serialization and deserialization round-trip

API and Format

No API or format changes.

Documentation

No documentation changes

Generative AI tooling

[leaves12138]

Thanks for adding the utility modules. I found a blocking issue in PathUtil: NormalizePath currently turns valid URI paths without an authority, such as file:///tmp or hdfs:///warehouse, into file:/tmp / hdfs:/warehouse. In URI syntax the triple slash is significant here because it means an empty authority plus an absolute path; collapsing it changes the URI shape and can break filesystem/catalog path handling. Please preserve the scheme:///path form when the input has an explicit empty authority, and add tests for file:///.../hdfs:///... normalization.