Normalize HTTP error handling across SGS, Currency, and OData

[wilsonfreitas]

Context

HTTP behavior is inconsistent across modules. bcb/http.py defines shared clients and retry helpers, but feature modules import _CLIENT and _ASYNC_CLIENT directly and each module handles response failures differently.

Scope

Introduce one shared HTTP response handling approach for sync and async requests. Normalize status handling for 429, 404, 5xx, timeout, and connection failures.

Branching

Create the implementation branch from project-health-hardening and merge the fix back into project-health-hardening before any merge to main.

Acceptance Criteria

• SGS, Currency, and OData use a consistent error mapping strategy.
• Existing public exceptions remain backward compatible where possible.
• Tests cover 429, 404, 5xx, timeout, and malformed response cases.
• uv run pytest -m "not integration", Ruff, and mypy pass.

[wilsonfreitas]

Completed by PR #46, merged into project-health-hardening.