Retry v6 push registration after identity rejection

[czien]

Summary

Retry v6 register_push_token once when the cached Mega identity is rejected with CODE_NEED_NEGOTIATE_KEY or CODE_SIGNATURE_ERROR, then persist the refreshed Mega session after successful push registration.

Why

When the cached v6/Mega identity is stale, register_push_token can fail even though the account still has a valid Mega auth session. MegaHTTPApi.signedPost already clears cached identities for these response codes, so retrying the push-token registration lets the second attempt perform a fresh key exchange and register successfully.

Persisting the session after a successful push registration keeps the refreshed identity available for later startups.

Validation

• Focused Jest test:
  npm test -- --runTestsByPath src/http/__test__/megaApiPushSelector.test.tsx --runInBand
• Direct TypeScript compile:
  ./node_modules/.bin/tsc -p tsconfig.build.json
• Prettier check:
  ./node_modules/.bin/prettier --check src/http/megaTransition.ts src/http/__test__/megaApiPushSelector.test.tsx

Also validated against a real Home Assistant Eufy WS add-on setup where v6 push registration recovered and doorbell ring events began reaching the original ringing sensor after this patch.

[github-actions]

Thanks for your contribution! 🙏

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gh pr edit 958 --base develop

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