Optimize async I/O and locking patterns to reduce runtime blocking

[Copilot]

Identified and fixed performance bottlenecks: blocking file I/O in async contexts and inefficient locking for read-heavy credential access.

Changes

Replace blocking filesystem operations with async equivalents

• api/update.rs: Use tokio::fs::write instead of std::fs::write when writing update manifests
• recording.rs: Convert JrecManifest::{read_from_file, save_to_file} to async methods using tokio::fs
• service.rs: Make load_jrl_from_disk async to use tokio::fs::read_to_string

Before:

std::fs::write(updater_file_path, update_json).map_err(...)?;

After:

tokio::fs::write(updater_file_path, update_json).await.map_err(...)?;

Use RwLock for credential store to enable concurrent reads

• credential.rs: Replace Arc<Mutex<CredentialStore>> with Arc<RwLock<CredentialStore>>
• Read operations (.get()) use .read() lock, allowing concurrent credential lookups
• Write operations (.insert(), cleanup task) use .write() lock

Optimize byte array conversion in plugin manager

• plugin_manager/recording.rs: Change iter().map(|e| *e) to into_iter().map(|e| e) to eliminate unnecessary dereferencing

Original prompt

Identify and suggest improvements to slow or inefficient code

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