Perf: Replace TwigNode vector with BTreeMap

[arriqaaq]

Description

The current issue with versioning was due to the usage of vector inside a twignode to maintain all versions. As the vector grows larger, this was taking significant time and became worse as reported during surrealkv reload. This PR replaces the vector with a btreemap, and adds a reverse map from timestamp to version to make timestamp queries faster. There is a significant improvement as you can see.

But this comes at a cost of slow down in insertion time. Keeping the PR for future reference.

on main:

Insertion time for 1M key-version pairs: 4.630727792s

Each query type will be executed 1 times
Tree contains 100 keys with 10000 versions each

Results:
Query Type                Total Time      Avg Time  
--------------------------------------------------
LatestByVersion           64.542µs 64.542µs
LatestByTs                7.375µs 7.375µs
LastLessThanTs            3.917µs 3.917µs
LastLessOrEqualTs         3.042µs 3.042µs
FirstGreaterThanTs        7.125µs 7.125µs
FirstGreaterOrEqualTs     3.166µs 3.166µs

on this branch:

Insertion time for 1M key-version pairs: 81.642150042s

Each query type will be executed 1 times
Tree contains 100 keys with 10000 versions each

Results:
Query Type                Total Time      Avg Time  
--------------------------------------------------
LatestByVersion           229.25µs 229.25µs
LatestByTs                186.625µs 186.625µs
LastLessThanTs            182.292µs 182.292µs
LastLessOrEqualTs         180.875µs 180.875µs
FirstGreaterThanTs        173.625µs 173.625µs
FirstGreaterOrEqualTs     172.917µs 172.917µs