Fix MT5 initialization and sdist bug regressions

[dceoy]

Summary

• preserve initialization credentials even when Mt5Client.initialize() is called without a terminal path
• make Mt5DataClient context managers honor Mt5Config and retry_count, and handle version() None results as Mt5RuntimeError
• honor positional skip_to_datetime / index_keys decorator arguments and move sdist file selection to hatchling

Testing

• uv run pytest
• uv run ruff check .
• uv run pyright .
• uv build
• inspected the built sdist to confirm it excludes tests, uv.lock, .github, and .agents

Fixes #89
Fixes #90
Fixes #91
Fixes #92
Fixes #94

[chatgpt-codex-connector]

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[dceoy]

Reviewed the current head after the follow-up fix. No blocking issues found.

Checked:

• Mt5Client.initialize() now forwards credentials/timeout without path.
• Mt5DataClient.__enter__() now uses config-aware initialization and retry flow.
• failed/exception login paths shut down the initialized MT5 session before raising/retrying.
• version() now normalizes None responses to Mt5RuntimeError.
• positional skip_to_datetime / index_keys are now honored through signature binding.
• hatchling sdist selection is aligned with the active build backend.

CI/CD is green on the latest commit.