add calc_stored_meta_us metric

[jeffwashington]

Problem

metrics for shrink are missing lower level data for a section of store.

Summary of Changes

add metric for missing time

Fixes #

[codecov]

Codecov Report

Merging #17318 (4141faf) into master (a3c0833) will decrease coverage by 0.0%.
The diff coverage is 100.0%.

@@            Coverage Diff            @@
##           master   #17318     +/-   ##
=========================================
- Coverage    82.7%    82.7%   -0.1%     
=========================================
  Files         421      421             
  Lines      118064   118070      +6     
=========================================
- Hits        97687    97675     -12     
- Misses      20377    20395     +18     

[jeffwashington]

here's some data where I added it in temporarily to the shrink_stats metrics:
shrink_stats num_slots_shrunk=2989i storage_read_elapsed=0i index_read_elapsed=309356i find_alive_elapsed=10085i create_and_insert_store_elapsed=56001i store_accounts_elapsed=353106i update_index_elapsed=180224i handle_reclaims_elapsed=88388i write_storage_elapsed=0i rewrite_elapsed=696774i drop_storage_entries_elapsed=84i recycle_stores_write_time=360i accounts_removed=4164i bytes_removed=2875392i store_append_accounts=161879i store_find_store=0i store_hash_accounts=0i build_meta_time=166724i read_only_cache=128213i