feat: allow users to configure max cache bytes

[bruce-y]

GC flag being disabled causes buildkit to not track last access times. It looks like the max-age option for buildctl overrides any additional options, especially when all of the last accessed values are unset. Disabling this option and only setting max cache size sidesteps this issue.

  ID									RECLAIMABLE	SIZE		LAST ACCESSED
  mgza1bb6tgrhvcb9p6qwjkd3m*                                             	true       	4.10kB		
  puqpq6frx7mn9qmmy4upjhps1*                                             	true       	8.19kB		
  u7xd5e7f1db226w56r91xdji4                                              	true       	8.22kB		
  9dv1zm7rkwd5b2otf2etfrwit                                              	true       	8.31kB		
  q57yee1rx33m6usoo805kjzbp                                              	true       	12.42kB		
  yxus1lvhnfbkgqlyveyjjypuk                                              	true       	16.50kB		
  tgir6bk9qgzuqfk5rsz2td8ru                                              	true       	16.57kB		
  qqf1ths8zwwljx2qtysegvdbi                                              	true       	20.65kB		
  72ajqijwmzmxq361ole36u5ky                                              	true       	27.72kB		
  6nihfcm6ryienxzb86lzfonwf                                              	true       	42.70kB		
  f1ruc4ze87pmsa2w6xv8r34i9                                              	true       	54.42kB		
  osjgpumxh8by8uak1x8a8d3so                                              	true       	116.89kB	
  db63u1g20lw5jmv8yx24bbkdm                                              	true       	5.00MB		
  k95bul72rhsjvl3k5gocqm53x                                              	true       	5.13MB		
  nf5fg6nhcvbesymd7r28kmxdx                                              	true       	23.39MB		
  61fvglf7bpwfxje9x5yq2atwh                                              	true       	35.50MB		
  pyu1wrhv7dlzegazwm9gxwlqk                                              	true       	117.19MB	
  znun8miypkycre8ux12w8y4sg                                              	true       	268.50MB	
  tcbb16ybnv3e2te56mf8hni4v                                              	true       	268.50MB	
  1y0crk9isg6h2klukxov5l8g0                                              	true       	268.50MB	
  27o93rnfl5td8vb6a903zukr9                                              	true       	268.50MB	

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[adityamaru]

nice, much simpler

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

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