When objects hold a lot of read locks cleanup time grows exponentially.

```
BEFORE:

Unable to complete tests.

AFTER:

=== RUN   Test_localLocker_expireOldLocksExpire/100-locks/1-read
    local-locker_test.go:298: Scan Took: 0s. Left: 100/100
    local-locker_test.go:317: Expire 50% took: 0s. Left: 44/44
    local-locker_test.go:331: Expire rest took: 0s. Left: 0/0
=== RUN   Test_localLocker_expireOldLocksExpire/100-locks/100-read
    local-locker_test.go:298: Scan Took: 0s. Left: 10000/100
    local-locker_test.go:317: Expire 50% took: 1ms. Left: 5000/100
    local-locker_test.go:331: Expire rest took: 1ms. Left: 0/0
=== RUN   Test_localLocker_expireOldLocksExpire/100-locks/1000-read
    local-locker_test.go:298: Scan Took: 2ms. Left: 100000/100
    local-locker_test.go:317: Expire 50% took: 55ms. Left: 50038/100
    local-locker_test.go:331: Expire rest took: 29ms. Left: 0/0
=== RUN   Test_localLocker_expireOldLocksExpire/10000-locks/1-read
    local-locker_test.go:298: Scan Took: 1ms. Left: 10000/10000
    local-locker_test.go:317: Expire 50% took: 2ms. Left: 5019/5019
    local-locker_test.go:331: Expire rest took: 2ms. Left: 0/0
=== RUN   Test_localLocker_expireOldLocksExpire/10000-locks/100-read
    local-locker_test.go:298: Scan Took: 23ms. Left: 1000000/10000
    local-locker_test.go:317: Expire 50% took: 160ms. Left: 499798/10000
    local-locker_test.go:331: Expire rest took: 138ms. Left: 0/0
=== RUN   Test_localLocker_expireOldLocksExpire/10000-locks/1000-read
    local-locker_test.go:298: Scan Took: 200ms. Left: 10000000/10000
    local-locker_test.go:317: Expire 50% took: 5.888s. Left: 5000196/10000
    local-locker_test.go:331: Expire rest took: 3.417s. Left: 0/0
=== RUN   Test_localLocker_expireOldLocksExpire/1000000-locks/1-read
    local-locker_test.go:298: Scan Took: 133ms. Left: 1000000/1000000
    local-locker_test.go:317: Expire 50% took: 348ms. Left: 500255/500255
    local-locker_test.go:331: Expire rest took: 307ms. Left: 0/0
```