Blocking command support (BLPOP/BRPOP & BLMOVE)

[TalZaccai]

• Adding support for blocking commands in Garnet (for List and SortedSet objects)
• Implementing logic for BRPOP/BLPOP & BLMOVE commands

Still remaining to address in this PR:

• Block processing of further commands once a blocking command has been called
• Stop the main loop in CollectionItemBroker if there are no active observers
• Periodically clean up "zombie" observers (observers whose resp session has disposed but are still on the key's observer queue)
• Remove keys whose observer queues are empty
• Add more test cases

Added some website docs for the ItemBroker class here: website/docs/dev/collection-broker.md

[badrishc]

Please report BDN results of main vs. this branch for -f *.RespParseStress.*

[badrishc]

Added comments mostly related to allocations (both byte[] and Task) and potentially heavy code paths. We need to optimize for:

1. The case where BL* instructions are not used (i.e., heavy classes are created lazily)
2. Optional - avoid byte[] allocations by keeping items in FasterLog
3. Avoid Task allocations by using the async codepath only when no items available to process synchronously.

[TalZaccai]

Please report BDN results of main vs. this branch for -f *.RespParseStress.*

current branch:

Method	Job	EnvironmentVariables	Runtime	Mean	Error	StdDev	Allocated
InlinePing	.NET 6	Empty	.NET 6.0	3.736 us	0.0444 us	0.0394 us	-
Set	.NET 6	Empty	.NET 6.0	40.151 us	0.5339 us	0.4994 us	-
SetEx	.NET 6	Empty	.NET 6.0	49.062 us	0.9620 us	0.8033 us	-
Get	.NET 6	Empty	.NET 6.0	23.247 us	0.4078 us	0.3815 us	-
ZAddRem	.NET 6	Empty	.NET 6.0	203.544 us	3.8383 us	3.5903 us	23552 B
InlinePing	.NET 8	DOTNET_TieredPGO=0	.NET 8.0	3.246 us	0.0126 us	0.0098 us	-
Set	.NET 8	DOTNET_TieredPGO=0	.NET 8.0	27.550 us	0.0505 us	0.0394 us	-
SetEx	.NET 8	DOTNET_TieredPGO=0	.NET 8.0	38.817 us	0.4597 us	0.4300 us	-
Get	.NET 8	DOTNET_TieredPGO=0	.NET 8.0	17.808 us	0.1461 us	0.1296 us	-
ZAddRem	.NET 8	DOTNET_TieredPGO=0	.NET 8.0	167.105 us	3.1375 us	2.7813 us	23552 B

main:

Method	Job	EnvironmentVariables	Runtime	Mean	Error	StdDev	Allocated
InlinePing	.NET 6	Empty	.NET 6.0	3.461 us	0.0321 us	0.0268 us	-
Set	.NET 6	Empty	.NET 6.0	38.975 us	0.7435 us	0.7302 us	-
SetEx	.NET 6	Empty	.NET 6.0	50.464 us	0.3800 us	0.3173 us	-
Get	.NET 6	Empty	.NET 6.0	22.726 us	0.1165 us	0.0910 us	-
ZAddRem	.NET 6	Empty	.NET 6.0	195.731 us	1.7133 us	1.4307 us	23552 B
InlinePing	.NET 8	DOTNET_TieredPGO=0	.NET 8.0	3.376 us	0.0247 us	0.0219 us	-
Set	.NET 8	DOTNET_TieredPGO=0	.NET 8.0	27.949 us	0.1557 us	0.1300 us	-
SetEx	.NET 8	DOTNET_TieredPGO=0	.NET 8.0	38.309 us	0.2966 us	0.2774 us	-
Get	.NET 8	DOTNET_TieredPGO=0	.NET 8.0	18.324 us	0.1501 us	0.1404 us	-
ZAddRem	.NET 8	DOTNET_TieredPGO=0	.NET 8.0	165.709 us	3.2412 us	4.9496 us	23552 B