buffers data shreds to make larger erasure coded sets (bp #15849)

[mergify]

This is an automatic backport of pull request #15849 done by Mergify.

Cherry-pick of 4f82b89 has failed:

On branch mergify/bp/v1.6/pr-15849
Your branch is up to date with 'origin/v1.6'.

You are currently cherry-picking commit 4f82b897b.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   core/benches/shredder.rs
	modified:   core/src/broadcast_stage.rs
	modified:   core/src/broadcast_stage/broadcast_utils.rs
	modified:   core/src/broadcast_stage/standard_broadcast_run.rs
	modified:   core/src/shred_fetch_stage.rs
	modified:   ledger/src/blockstore.rs

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   ledger/src/shred.rs

To fixup this pull request, you can check out it locally. See documentation: https://help.github.com/articles/checking-out-pull-requests-locally/

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[mergify]

automerge label removed due to a CI failure

[behzadnouri]

@Mergifyio rebase

[mergify]

Command rebase: success

Branch has been successfully rebased

[mergify]

automerge label removed due to a CI failure

[codecov]

Codecov Report

Merging #16074 (818775c) into v1.6 (a04ca03) will increase coverage by 0.0%.
The diff coverage is 88.8%.

@@           Coverage Diff           @@
##             v1.6   #16074   +/-   ##
=======================================
  Coverage    79.9%    79.9%           
=======================================
  Files         409      409           
  Lines      107349   107443   +94     
=======================================
+ Hits        85779    85862   +83     
- Misses      21570    21581   +11