Improve event handling on macOS and Windows

[liamcmitchell]

Hi, I came across #111 and similar issues on macOS.

• on win, card add/remove is often missed
• on mac, if started with attached reader and inserted card, card removed is incorrectly emitted a second later (caused by your recent fixes?)

The following changes fix the issues for me:

• added a small retry when a card is inserted, so brief reader-list delays don’t cause misses
• cleaned up compiler warnings with explicit casts
• updated card presence when reader lists change (PnP)
• made reader/card state handling more reliable during reader add/remove churn
• improved refresh logic for already-known readers
• changed JS callback delivery to non-blocking to avoid shutdown stalls/deadlocks

Tested on Linux/macOS/Windows with node dist/examples/monitor-cards.js.