fix: error code 100 (exceed max member)

[highesttt]

No description provided.

[linear-code]

PLAT-38687

[indent]

PR Summary

Handles LINE TalkException code:100 "exceed max member" so that sends to groups too large for E2EE key registration fall back to plaintext (matching LINE's own behavior) instead of surfacing a hard error.

• IsNoUsableE2EEGroupKey (raw-error-string path): adds a code-100 branch gated on an exact "reason":"exceed max member" match, and switches the envelope guard from a literal "code":10051 check to the shared hasResponseErrorCode helper.
• isNoUsableE2EEGroupKeyTalkException (structured path): adds code == 100 && reason == "exceed max member".
• Adds tests covering the positive case, a code-100 with a different reason, the phrase appearing outside the reason field, and the structured path, plus a lineGroupE2EEFetchFailureError test asserting the oversized-group error allows plaintext fallback.

Issues

No issues found.

CI Checks

All CI checks passed on f6cde3d.