mlx-native 0.15.3

What's Changed

• test(memory): distinguish resource and device allocation metrics by @robertelee78 in #48
• test(memory): probe bounded tracked shared Metal heaps by @robertelee78 in #49
• feat(memory): add optional fixed-heap buffer pool by @robertelee78 in #50
• fix(metal): qualify attention tile thread receivers; prepare 0.15.3 by @robertelee78 in #51
• refactor(metal): share checked chunk arena allocation plan by @robertelee78 in #52
• feat(memory): bound legacy pool cold growth with shared quotas by @robertelee78 in #55
• perf(indexer): prepare query-tiled MMA dispatch with smaller workspace by @robertelee78 in #56

Full Changelog: v0.15.2...v0.15.3