fix: add copy_rates_from_pos_as_df fallback for trading client rate fetch (#88)

* fix: add copy_rates_from_pos_as_df fallback in fetch_latest_closed_rates_for_trading_client

Mt5DataClient (returned by create_trading_client) exposes copy_rates_from_pos_as_df,
not fetch_latest_rates_as_df. Adds a fallback path that resolves the granularity string
to an integer timeframe via parse_timeframe, fetches count+1 bars from start_pos=0,
and applies the same drop_forming_rate_bar + tail(count) logic so callers that use
the client returned by create_trading_client no longer need a compatibility shim.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* Bump version to v1.0.3

* fix: hoist parse_timeframe before dispatch and add invalid-granularity test

Hoisting parse_timeframe(granularity) before the fetch_latest_rates_as_df /
copy_rates_from_pos_as_df dispatch ensures invalid granularity strings fail
consistently on both paths with a clear ValueError, rather than only when
the fallback branch is taken.

Adds test_copy_rates_from_pos_fallback_raises_on_invalid_granularity to pin
the early-validation contract and confirm the underlying method is never called.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

---------

Co-authored-by: agent <agent@localhost>
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "mt5cli"
-version = "1.0.2"
+version = "1.0.3"
 description = "Generic MT5 data and execution infrastructure for Python applications"
 authors = [{name = "dceoy", email = "dceoy@users.noreply.github.com"}]
 maintainers = [{name = "dceoy", email = "dceoy@users.noreply.github.com"}]