perf: Improve start up time

[Veykril]

• Rowan's green nodes are super drop heavy and as lru eviction happens on cancellation this can block for quite some time, especially after cache priming
• Likewise the span map dropping is fairly heavy, so we offload that too
• Delay initial cache priming until proc macros are loaded as we otherwise load up a bunch of garbage (stale IDs) into salsa
• in crate graph construction we were repeatedly probing the cargo binary path for every crate, thats done once now (and also more correctly)
• Lastly we also now prime the crate lang item queries, as those will be hit by the symbol map which will otherwise walk the entire crate dependency tree in a single worker again, making our parallel efforts partially pointless