fill on warmup

[bitfaster]

When starting from an empty state, the warm queue is only populated when items are accessed more than once. The default partition now allocates 80% to warm. During warmup, the warm queue can stay empty and available capacity goes unused.

This PR uses a different strategy during warmup to fill the warm queue, enabling the cache to reach a full state.

[bitfaster]

This significantly improves hit rate

Glimpse

CacheSize	ConcurrentLruHitRate	ClassicLruHitRate
250	12.834580216126351	0.914380714879468
500	26.134663341645886	0.9476309226932668
750	39.43474646716542	1.14713216957606
1000	43.275145469659186	11.205320033250207
1250	49.925187032418954	21.24688279301746
1500	52.40232751454697	36.55860349127182
1750	53.49958437240233	45.03740648379053
2000	53.54945968412302	57.40648379052369

Arc Search (S3)

CacheSize	ConcurrentLruHitRate	ClassicLruHitRate
100000	9.630056664851665	2.3273947808169604
200000	18.70513616105412	4.631702842969722
300000	26.836933045224736	7.589191953876295
400000	34.39737021064863	12.038846146766927
500000	41.43631448206458	22.76700295995137
600000	48.27514541646356	34.630065806899715
700000	54.612297322318504	46.042754798935285
800000	61.295719534642934	56.599784662105634

Arc OLTP

CacheSize	ConcurrentLruHitRate	ClassicLruHitRate
250	15.629686756477366	16.473425988218498
500	27.128847174135394	23.445405269404745
750	32.290829135421625	28.28074320813438
1000	36.014417843996306	32.83089663018449
1250	38.6823753343288	36.209682271412085
1500	40.69409119997375	38.69604931383971
1750	42.47695934452412	40.7881681790088
2000	44.16925104879423	42.46973948334236

Arc Database

CacheSize	ConcurrentLruHitRate	ClassicLruHitRate
1000000	11.94732984541647	3.0858932571504036
2000000	23.242502873642838	10.744535536786323
3000000	36.190929184521515	18.5903853197138
4000000	39.605386837046645	20.244791789054513
5000000	45.15375010247688	21.031951531197397
6000000	50.37196791697349	33.95308575711706
7000000	56.082914488987626	38.8978587542623
8000000	61.00455968643755	43.03472380114861