feat(client): allow specifying `history_length` via call-site `MessageSendConfiguration` in `BaseClient.send_message`#500

sokoliva merged 16 commits intoa2aproject:maina2aproject/a2a-python:mainfrom

TadakiAsechi:feat/client-send-message-config-mergeTadakiAsechi/a2a-python:feat/client-send-message-config-mergeCopy head branch name to clipboard