Retry transient shared contact profile downloads

[Xare123]

Summary

• Classify shared-profile download failures as transient or permanent
• Retry transient network and service failures with a bounded policy
• Suppress duplicate schedules and reset state after a successful completion

Why

Temporary relay or network failures should not permanently prevent a shared contact profile from loading, while malformed or permanent failures should not retry forever.

Validation

• lutter test test/services/rustpush/profile_retry_policy_test.dart --reporter expanded
• 4 of 4 focused tests passed
• git diff --check passed

Scope

The retry policy is limited to shared contact profile downloads.

[Xare123]

Superseded by #250. The send and shared-profile retry changes both modify the same RustPush service lifecycle and conflict when merged independently, so they were combined into one tested review unit. The combined policy suite passes 9 of 9 focused tests.