Make hamt value type generic and add benchmarks

[austinabell]

Summary of changes
Changes introduced in this pull request:

• Seems like this is the best solution for Optimize HAMT to not deserialize values internally #391. Previously, there was multiple value types in one hamt, but that is not the case anymore it seems and we cannot leave bytes serialized when using Serde (go implementation uses a deferred type for this which avoids deserializing until needed but this is almost impossible without replacing serde for serialization for the hamt).
• Adds benchmarks to the hamt

This will be pointed at hashing branch until #624 comes in (didn't want to deal with conflicts) and I will open when it's pointing back at main

benchmarks:

HAMT bulk insert (no flush)
                        time:   [39.967 us 40.263 us 40.560 us]
                        change: [-63.784% -63.178% -62.603%] (p = 0.00 < 0.05)
                        Performance has improved.

HAMT bulk insert with flushing and loading
                        time:   [2.2143 ms 2.2285 ms 2.2429 ms]
                        change: [-65.130% -64.540% -64.033%] (p = 0.00 < 0.05)
                        Performance has improved.

HAMT deleting all nodes time:   [75.801 us 76.273 us 76.734 us]
                        change: [-71.930% -71.549% -71.206%] (p = 0.00 < 0.05)
                        Performance has improved.

HAMT for_each function  time:   [58.529 us 59.057 us 59.562 us]
                        change: [-84.056% -83.806% -83.585%] (p = 0.00 < 0.05)
                        Performance has improved.

Reference issue to close (if applicable)

Closes #202
Closes #391

Other information and links

[dutterbutter]

Not that is matters too much but the latest version 0.3.3 I believe.

[austinabell]

patch versions get automatically bumped to the most up to date (if you look inside of the Cargo.lock you'll see the version is actually 0.3.3) but I will update this for peace of mind