refactor client tracking, fix atomicity, squashing and multi/exec

[kostasrim]

• add partial support for CLIENT CACHING TRUE (only to be used with TRACKING OPTIN)
• add OPTIN to CLIENT TRACKING command
• refactor client tracking to respect transactional atomicity
• fixed multi/exec and disabled squashing with client tracking
• add tests

Resolves #2969, #2971, #2997, #2998

P.s. All tests in rueidis TestSingleClientIntegration pass except pub/sub because we don't yet support it see #3001

[dranikpg]

there is a deeper problem with CLIENT TRACKING OPTIN

suppose you have

MULTI
CLIENT TRACKING OPTIN
GET A
GET B 
GET C
EXEC

Now, if you squash the last 3, you loose the order - becuase GET C can run first of those three

[romange]

lets reject CLIENT TRACKING OPTIN in multi

[romange]

in fact, should we even allow CLIENT commands inside MULTI?

[kostasrim]

in fact, should we even allow CLIENT commands inside MULTI?

Only CLIENT CACHING YES as it has specific semantics