Speed up -AAA on large snapshots without changing its results

[fatalSec]

On a 37,863-function Dart 3.13 iOS app r2flutter -AAA took 19 minutes (1,136s).

Three costs grew with snapshot size:

• read_mem cached a single 1 MB window. modern_load_rodata_strings alternates between a cluster alloc stream and the RO data image megabytes away, so each string refilled the window twice (a 1 MB read plus the 0xff fill r_io_bank_read_at does first). Keep four windows with LRU eviction. Move the cache behind a pointer so DartCtx copies (flutter_model_load, dart_recovery_model_load) share buffers together with their addresses instead of leaving the original with stale ones, and drop a window whose refill failed since the failed read already overwrote it. -f 12.4s -> 0.5s; -c/-i/-T/-S ~6s -> <0.25s.

• afs stores prototypes through r_anal_save_parsed_type, which calls r_anal_remove_parsed_type for each declared type. For an existing name that sorts and scans the whole type database although r_type_del has already removed every key of a function type. Names repeat often: anonymous closures, and names the C parser cuts at ':' (dyn:call is stored as call). Parse the prototype with r_anal_cparse and r_type_del those names first so afs takes its early return. The signature pass went from 1,127s to 27s.

• With anal.trycatch (the radare2 6.2.2 default) every af walks all flags twice for try..catch|filter. After -AAA creates its flags that is O(flags) per function. Disable it around r2flutter's af loops when no try.* flag exists, which cannot change the result.

-AAA now takes 36s on that app (35s -> 6s on a smaller 3.13 build).