TalkTalk (UK) branded F5364 does not recognise the ModelNumber attribute
requested in GetDeviceInfo, which caused an exception because the response
handler threw for any ActionError. As a result HA could not connect to the
router to retrieve useful info, even though ModelNumber is not essential.

Fixed by:
 - Lifting ActionError handling out of the low-level POST into a dedicated
   ActionErrorHandler, so callers can react appropriately (and multiple
   actions can be handled individually, addressing the previous TODO).
 - Adding a suppress_action_errors option so get_value(s)_by_xpath can
   ignore unknown-path errors and return None for missing values, while
   still raising genuine errors (auth, etc.).
 - Using that option in get_device_info's fallback so missing DeviceInfo
   attributes are tolerated.

Existing error-raising behaviour is retained for all other calls, which now
invoke ActionErrorHandler.throw_if_error explicitly.

Tests cover the suppression behaviour of get_value(s)_by_xpath, the
end-to-end get_device_info fallback for the reported F5364 case, and the
ActionErrorHandler in isolation (throw_if_error / throw_if_error_at /
from_error_description).

Rebased onto upstream main, preserving the XPath-escaping fix (iMicknl#476),
get_logs, and the speed-test additions.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>