Fix InvalidSessionException treated as permanent auth failure

[arpena]

Summary

InvalidSessionException inherits from UnauthorizedException, which causes consumers (like the ha-sagemcom-fast integration) to treat transient session errors as permanent authorization failures.

Problem

When the router invalidates a session (e.g., due to a concurrent login from the web interface), the API raises InvalidSessionException. Because it inherits from UnauthorizedException, consumers that catch UnauthorizedException to detect permanent auth failures (like Home Assistant raising ConfigEntryAuthFailed) incorrectly treat this transient condition as "bad credentials", permanently disabling the integration.

Additionally, max_tries=1 on the backoff decorators means the on_backoff=retry_login handler fires but no actual retry occurs — the function is only called once.

Fix

1. Change exception hierarchy: InvalidSessionException now inherits from BaseSagemcomException instead of UnauthorizedException. This is a transient error, not a permanent auth failure.

2. Increase max_tries to 2: With max_tries=2, when an InvalidSessionException occurs, the backoff handler calls retry_login() and then retries the operation once before giving up.

Breaking Change Note

This is a minor breaking change for consumers that catch UnauthorizedException and expect InvalidSessionException to be included. Consumers should update to catch InvalidSessionException separately if they need to handle it. The ha-sagemcom-fast integration already has a PR to handle this.

Reproduction

1. Log in to the router web interface during an API poll cycle
2. The concurrent login invalidates the library's session
3. get_hosts() raises InvalidSessionException
4. Consumer catches it as UnauthorizedException → permanent failure

After this fix, the library retries the login and operation automatically.