fix: avoid rlimit side effect in docs example

[immanuwell]

What

Move the rlimit docs snippet out of package init. Importing docs/examples should not try to raise RLIMIT_MEMLOCK.

Repro

On an unprivileged shell:

go test ./... -run TestDoesNotExist

Before: docs/examples panics in init with failed to set memlock rlimit: operation not permitted.

After: passes, no test is selected. Small papercut

Checks

go test ./docs/examples -run TestDoesNotExist
go test ./... -run TestDoesNotExist
go build ./...
go test -c -o /dev/null ./...