Improve extra item aura refresh timing for fishing buffs

[thllxb]

Summary

This PR updates extra item and macro aura refresh behavior so Angleur can reapply before the buff fully expires, using fishing channel timing instead of waiting for aura removal.

Closes #30.

Changes

• add shared extra-item aura reuse logic for retail and classic variants
• refresh extra items and macros when remaining aura time drops below the refresh threshold instead of only after expiration
• measure the fishing channel duration from UnitChannelInfo("player") and use that as the preferred refresh threshold
• fall back to a 30 second threshold when no live fishing channel duration is available
• clear cached channel duration on failed reads so stale timing data is not reused
• add a standalone Lua regression script covering fallback and dynamic-threshold behavior

Validation

• editor diagnostics show no errors in the changed Lua files
• standalone Lua regression script was updated, but could not be executed in this workspace because no lua or luajit runtime is available on PATH

[thllxb]

@LegolandoBloom Can you please review and merge?