Panic when using expirable cache

[kalafut]

When testing with an expirable.LRU, I've seen the crash below. I was using size=100 and expiration=1 second, and the access pattern was all around a single key. The test had a couple concurrent reads per second, and a write of the same key any time there was a cache miss. I'd reliably hit this panic after a few seconds.

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x2 addr=0x0 pc=0x102c011b8]

goroutine 21 [running]:
github.com/hashicorp/golang-lru/v2/internal.(*LruList[...]).Remove(...)
	/Users/kalafut/go/pkg/mod/github.com/hashicorp/golang-lru/[email protected]/internal/list.go:97
github.com/hashicorp/golang-lru/v2/expirable.(*LRU[...]).removeElement(0x140001c6ff0?, 0x1400020aea8?)
	/Users/kalafut/go/pkg/mod/github.com/hashicorp/golang-lru/[email protected]/expirable/expirable_lru.go:298 +0x28
github.com/hashicorp/golang-lru/v2/expirable.(*LRU[...]).deleteExpired(0x102fb2c20)
	/Users/kalafut/go/pkg/mod/github.com/hashicorp/golang-lru/[email protected]/expirable/expirable_lru.go:319 +0x20c
github.com/hashicorp/golang-lru/v2/expirable.NewLRU[...].func1()
	/Users/kalafut/go/pkg/mod/github.com/hashicorp/golang-lru/[email protected]/expirable/expirable_lru.go:90 +0xa0
created by github.com/hashicorp/golang-lru/v2/expirable.NewLRU[...] in goroutine 1
	/Users/kalafut/go/pkg/mod/github.com/hashicorp/golang-lru/[email protected]/expirable/expirable_lru.go:82 +0x2b8
exit status 2