Sqlite pooling for connections and commands

[adamhathcock]

Adds a pool for sqlite connections and commands to reduce creations. Dispose is needed for the pool.

Requires #194

[codecov]

Codecov Report

Attention: Patch coverage is 91.30435% with 22 lines in your changes missing coverage. Please review.

Project coverage is 68.08%. Comparing base (11fe8e8) to head (5646766).
Report is 1 commits behind head on dev.

Files with missing lines	Patch %	Lines
src/Speckle.Sdk/Credentials/AccountManager.cs	28.57%	5 Missing ⚠️
src/Speckle.Sdk/SQLite/CacheDbCommandPool.cs	94.64%	2 Missing and 1 partial ⚠️
src/Speckle.Sdk/Serialisation/V2/Send/BaseItem.cs	40.00%	3 Missing ⚠️
...k/Serialisation/V2/DummySendServerObjectManager.cs	0.00%	2 Missing ⚠️
...le.Sdk/Serialisation/V2/SerializeProcessFactory.cs	50.00%	2 Missing ⚠️
...peckle.Sdk/SQLite/SqLiteJsonCacheManagerFactory.cs	66.66%	1 Missing ⚠️
...Sdk/Serialisation/V2/ServerObjectManagerFactory.cs	50.00%	1 Missing ⚠️
...s/Speckle.Sdk.Serialization.Tests/DetachedTests.cs	50.00%	1 Missing ⚠️
...k.Serialization.Tests/DummySqLiteReceiveManager.cs	50.00%	1 Missing ⚠️
....Sdk.Serialization.Tests/DummySqLiteSendManager.cs	50.00%	1 Missing ⚠️
... and 2 more

Additional details and impacted files

@@             Coverage Diff             @@
##              dev     #193       +/-   ##
===========================================
+ Coverage   55.12%   68.08%   +12.96%     
===========================================
  Files         239      260       +21     
  Lines        9730    10526      +796     
  Branches     1076     1087       +11     
===========================================
+ Hits         5364     7167     +1803     
+ Misses       4113     3011     -1102     
- Partials      253      348       +95     

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[JR-Morgan]

LGTM, but I want to bench mark these changes