docs(python): add doctests to builder and config APIs, enable --doctest-modules

[GayathriSrividya]

Summary

Closes #82.

This PR implements the doctest setup designed by @xushiyan in the issue.

Sets up Python doctest infrastructure and adds runnable Examples: blocks to the public Python API. The blocking dependency (#141 — consolidate testing data modules) was resolved in release 0.5.0.

Changes

python/pyproject.toml

Add addopts = "--doctest-modules" to [tool.pytest.ini_options]. The hudi/ directory was already in testpaths; this flag activates doctest discovery so the examples in docstrings are collected and run as part of pytest.

python/hudi/table/builder.py

Add Examples: blocks to every public HudiTableBuilder method (as specified by @xushiyan — "guiding example to show users the most typical use cases of the APIs and actual test cases like other unit tests"):

Method	What the doctest covers
from_base_uri	Creates a builder; asserts base_uri, empty hudi_options, empty storage_options
with_hudi_option	Adds a single Hudi key; asserts hudi_options dict
with_hudi_options	Adds multiple Hudi keys at once; uses sorted() for determinism
with_storage_option	Adds a single storage key; asserts storage_options dict
with_storage_options	Adds multiple storage keys at once
with_option	Adds a generic key to options
with_options	Adds multiple generic keys
build	Shows the full builder chain; uses # doctest: +SKIP since a real table path is required

python/hudi/_config.py

Add Examples: blocks to the three config enums, demonstrating how to read the canonical key string from an enum member:

>>> from hudi import HudiTableConfig
>>> HudiTableConfig.BASE_PATH.value
'hoodie.base.path'

Key values were verified against the Rust AsRef<str> implementations in crates/core/src/config/{table,read,plan}.rs.