stop padding new append vecs to page size

[jeffwashington]

Problem

We no longer 'append' to append vecs. We know the full size when we are ready to write to them. So, it is no longer necessary to pad them to the next full page size. This makes 100% of the data in the file required and the used length equal to the allocated length.

Summary of Changes

Fixes #

[HaoranYi]

seems a bench test failed.

[2023-10-09T23:01:42.809916369Z ERROR solana_accounts_bench] results different:

  | (AccountsHash(3T99DHTbjqBrqnUEBzAng7rZgdyVDwDNf5eY4HGR6pHi), 12505000)
  | (AccountsHash(GKot5hBsd81kMupNCXHaqbhv3huEbxAFMLnpcX2hniwn), 0)
  | hash,3T99DHTbjqBrqnUEBzAng7rZgdyVDwDNf5eY4HGR6pHi,hash took 16ms,hash using store took 25ms,151%

[codecov]

Codecov Report

Merging #33607 (cec2e55) into master (1d91b60) will increase coverage by 0.0%.
Report is 9 commits behind head on master.
The diff coverage is 92.1%.

@@           Coverage Diff           @@
##           master   #33607   +/-   ##
=======================================
  Coverage    81.7%    81.7%           
=======================================
  Files         807      807           
  Lines      218252   218263   +11     
=======================================
+ Hits       178438   178456   +18     
+ Misses      39814    39807    -7     

[HaoranYi]

lgtm