The split managed one ordering constraint: arena_choose() had to be
defined before arena_choose_maybe_huge() but after the tsd/tcache
inlines it depends on. After the malloc_dispatch refactor moved the
heaviest tcache-pulling inlines out of arena_inlines_b.h, the
remaining arena-side inlines all belong together. The merged
arena_inlines.h explicitly includes jemalloc_internal_inlines_a.h
and tcache.h (previously transitively pulled).
Convert the production source files in src/ (69 .c/.cpp) and
test/jemalloc_test.h.in to list the headers they actually use, then
delete the umbrella. Three consolidated headers (peak_event.h,
prof_sys.h, sz.h) also gain explicit transitive includes.
Every translation unit now declares what it uses. A missing include
now fails at the failing file rather than silently working because
something upstream pulled in the world.
Drop the duplicate arena->tcache_ql; stats merging walks the
cache_bin_array_descriptor_ql directly. Rename the protecting mutex
from tcache_ql_mtx to cache_bin_array_descriptor_ql_mtx to match. Add
an assertion in test_thread_migrate_arena that the dissociate-time
flush zeros cache_bin->tstats.nrequests.
