Add resilient multi-account orchestration helpers (#22)

* Add SDK orchestration helpers for resilient multi-account collection

- collect_latest_rates_for_accounts_with_retries(): exponential-backoff
  retries around collect_latest_rates_for_accounts(), retrying only
  Mt5TradingError/Mt5RuntimeError and re-raising on exhaustion.
- resolve_account_spec()/resolve_account_specs() and
  substitute_env_placeholders(): merge explicit overrides over AccountSpec
  fields and expand ${ENV_VAR} placeholders, raising ValueError on missing
  variables.
- ThrottledHistoryUpdater: monotonic-clock throttled wrapper around
  update_history() with should_update()/update() and opt-in suppress_errors.
- load_rate_series_by_granularity(): rate-series loader keyed by
  (symbol | None, granularity_name).
- Export new APIs, add unit tests (100% coverage), and document in README
  and docs/api.

* chore: bump version from 0.5.1 to 0.5.3 (#24)

Co-authored-by: Cursor Agent <cursoragent@cursor.com>
Co-authored-by: Daichi Narushima <dceoy@users.noreply.github.com>

* fix: resolve leftover merge conflict markers in version files

Co-authored-by: Daichi Narushima <dceoy@users.noreply.github.com>

* fix: address PR review feedback on SDK orchestration helpers

- Use single-pass env substitution to avoid TOCTOU KeyError
- Apply backoff_base to all retry delays (backoff_base ** (attempt + 1))
- Preserve integer logins in resolve_account_spec; hide login in repr
- Fix docs examples (env ordering, while True loop, backoff comment)
- Parametrize suppress_errors tests for MT5 and SQLite errors

Co-authored-by: Daichi Narushima <dceoy@users.noreply.github.com>

---------

Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: Cursor Agent <cursoragent@cursor.com>
Co-authored-by: Daichi Narushima <dceoy@users.noreply.github.com>

pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "mt5cli"
-version = "0.5.2"
+version = "0.5.3"
 description = "Command-line tool for MetaTrader 5"
 authors = [{name = "dceoy", email = "dceoy@users.noreply.github.com"}]
 maintainers = [{name = "dceoy", email = "dceoy@users.noreply.github.com"}]