TLS exhaustion

I had a bug in hxcoro which caused too many TLS instances to be allocated, which resulted in a straight up segfault on MacOS HL. This was pretty hard to spot even for Claude, but he ultimately fixed it and said:

> macOS caps per-process pthread TLS keys at 512 (vs Linux's 1024), and HL never calls pthread_key_delete on GC. After ~170 test runs the keys were exhausted.

So at the very least this should fail more gracefully, but it also sounds like this is a general leak. I don't have a reproducible example because I don't have a mac, but a loop that just creates TLS instances should do it.