mvfs: Replace moka with lru due to memory leak

[losfair]

Seems that the moka crate has a memory leak issue when moka::sync::Cache is dropped. Detected in production, and confirmed with Valgrind:

==905778== 82,960 (560 direct, 82,400 indirect) bytes in 10 blocks are definitely lost in loss record 194 of 199
==905778==    at 0x483B7F3: malloc (in /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
==905778==    by 0x503005B: moka::sync_base::base_cache::BaseCache<K,V,S>::do_insert_with_hash::{{closure}} (in /home/ubuntu/Projects/mvsqlite/mvsqlite-preload/libmvsqlite_preload.so)
==905778==    by 0x502FD32: moka::cht::map::bucket::InsertOrModifyState<K,V,F>::into_insert_bucket (in /home/ubuntu/Projects/mvsqlite/mvsqlite-preload/libmvsqlite_preload.so)
==905778==    by 0x502CF77: moka::cht::map::bucket::BucketArray<K,V>::insert_or_modify (in /home/ubuntu/Projects/mvsqlite/mvsqlite-preload/libmvsqlite_preload.so)
==905778==    by 0x4BC49EE: moka::cht::map::bucket_array_ref::BucketArrayRef<K,V,S>::insert_with_or_modify_entry_and (in /home/ubuntu/Projects/mvsqlite/mvsqlite-preload/libmvsqlite_preload.so)
==905778==    by 0x503A7F6: moka::sync::cache::Cache<K,V,S>::insert (in /home/ubuntu/Projects/mvsqlite/mvsqlite-preload/libmvsqlite_preload.so)
==905778==    by 0x4BC8DDB: mvfs::vfs::Connection::insert_to_page_cache (in /home/ubuntu/Projects/mvsqlite/mvsqlite-preload/libmvsqlite_preload.so)
==905778==    by 0x4B08D3A: <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll (in /home/ubuntu/Projects/mvsqlite/mvsqlite-preload/libmvsqlite_preload.so)
==905778==    by 0x4B0A24A: _ZN97_$LT$core..future..from_generator..GenFuture$LT$T$GT$$u20$as$u20$core..future..future..Future$GT$4poll17h50e20491b908d0c9E.llvm.3961465344180881740 (in /home/ubuntu/Projects/mvsqlite/mvsqlite-preload/libmv
sqlite_preload.so)
==905778==    by 0x4B1042B: <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll (in /home/ubuntu/Projects/mvsqlite/mvsqlite-preload/libmvsqlite_preload.so)
==905778==    by 0x4A722A2: std::thread::local::LocalKey<T>::with (in /home/ubuntu/Projects/mvsqlite/mvsqlite-preload/libmvsqlite_preload.so)
==905778==    by 0x4A97131: tokio::park::thread::CachedParkThread::block_on (in /home/ubuntu/Projects/mvsqlite/mvsqlite-preload/libmvsqlite_preload.so)
==905778==
==905778== 165,920 (1,120 direct, 164,800 indirect) bytes in 20 blocks are definitely lost in loss record 197 of 199
==905778==    at 0x483B7F3: malloc (in /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
==905778==    by 0x503005B: moka::sync_base::base_cache::BaseCache<K,V,S>::do_insert_with_hash::{{closure}} (in /home/ubuntu/Projects/mvsqlite/mvsqlite-preload/libmvsqlite_preload.so)
==905778==    by 0x502FD32: moka::cht::map::bucket::InsertOrModifyState<K,V,F>::into_insert_bucket (in /home/ubuntu/Projects/mvsqlite/mvsqlite-preload/libmvsqlite_preload.so)
==905778==    by 0x502CF77: moka::cht::map::bucket::BucketArray<K,V>::insert_or_modify (in /home/ubuntu/Projects/mvsqlite/mvsqlite-preload/libmvsqlite_preload.so)
==905778==    by 0x4BC49EE: moka::cht::map::bucket_array_ref::BucketArrayRef<K,V,S>::insert_with_or_modify_entry_and (in /home/ubuntu/Projects/mvsqlite/mvsqlite-preload/libmvsqlite_preload.so)
==905778==    by 0x503A7F6: moka::sync::cache::Cache<K,V,S>::insert (in /home/ubuntu/Projects/mvsqlite/mvsqlite-preload/libmvsqlite_preload.so)
==905778==    by 0x4BC8DDB: mvfs::vfs::Connection::insert_to_page_cache (in /home/ubuntu/Projects/mvsqlite/mvsqlite-preload/libmvsqlite_preload.so)
==905778==    by 0x4B08D3A: <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll (in /home/ubuntu/Projects/mvsqlite/mvsqlite-preload/libmvsqlite_preload.so)
==905778==    by 0x4B0A24A: _ZN97_$LT$core..future..from_generator..GenFuture$LT$T$GT$$u20$as$u20$core..future..future..Future$GT$4poll17h50e20491b908d0c9E.llvm.3961465344180881740 (in /home/ubuntu/Projects/mvsqlite/mvsqlite-preload/libmv
sqlite_preload.so)
==905778==    by 0x4B11852: <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll (in /home/ubuntu/Projects/mvsqlite/mvsqlite-preload/libmvsqlite_preload.so)
==905778==    by 0x4A717CC: std::thread::local::LocalKey<T>::with (in /home/ubuntu/Projects/mvsqlite/mvsqlite-preload/libmvsqlite_preload.so)
==905778==    by 0x4A96D7E: tokio::park::thread::CachedParkThread::block_on (in /home/ubuntu/Projects/mvsqlite/mvsqlite-preload/libmvsqlite_preload.so)
==905778==

This PR replaces moka with lru to resolve the issue.

[losfair]

Related: moka-rs/moka#176