feat(logstore): support enable modify

[sls-dev-agent]

Summary

• add enable_logstore_modify for existing logstores
• expose enableModify through GetLogStoreResponse, defaulting to false
  when older responses omit the field
• add and update public type stubs
• bump the package version from 0.9.48 to 0.9.49

The enable request sends PUT /logstores/{logstore}/modification with
{"enabled":true}. A successful response means the asynchronous conversion
was accepted.

Testing

• python3 -m pytest tests/unit -q (40 passed, 8 skipped)
• python3 -m pytest tests/unit/test_logclient_mock.py tests/ci/build-test/ -q
  (17 passed)
• built wheel and verified version 0.9.49