refactor(imap): move resync request from Context to Imap

[link2xt]

For multiple transports we will need to run
multiple IMAP clients in parallel.
UID validity change detected by one IMAP client
should not result in UID resync
for another IMAP client.

[Copilot]

Pull Request Overview

This PR refactors the IMAP UID resync request mechanism from an atomic boolean flag to an async channel-based approach. The refactoring provides better decoupling by moving the resync request handling from the global Context into the IMAP module.

Key changes:

• Replaces AtomicBool with async_channel::bounded(1) for resync requests
• Removes Context::schedule_resync() method and migrates callers to use channel
• Removes unreachable address change detection code in configure.rs

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/context.rs	Removes atomic bool resync_request field and schedule_resync() method
src/imap.rs	Adds bounded async channel (sender/receiver) for resync requests
src/imap/session.rs	Adds resync_request_sender field to Session struct
src/imap/select_folder.rs	Replaces schedule_resync() calls with try_send() on channel
src/scheduler.rs	Updates resync request check from atomic swap to try_recv() on channel
src/configure.rs	Removes unreachable address change resync scheduling logic

Comments suppressed due to low confidence (1)

src/configure.rs:571

• [nitpick] The removed address change detection code (lines 568-576 in the old version) was unreachable because add_transport_inner() already prevents address changes at line 134-137. However, this removal is correct and simplifies the code by eliminating dead code. Consider adding a comment explaining that address changes are prevented earlier in the configuration flow if this is not obvious from context.

    let provider = configured_param.provider;
    configured_param
        .save_to_transports_table(ctx, param)
        .await?;

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