Just define BnakSlotDelta type alias (bp #8186)

[mergify]

This is an automated backport of pull request #8186 done by Mergify.io

Cherry-pick of 485806c has failed:

On branch mergify/bp/v0.23/pr-8186
Your branch is up to date with 'origin/v0.23'.

You are currently cherry-picking commit 485806c48.
  (fix conflicts and run "git cherry-pick --continue")
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Changes to be committed:

	modified:   core/src/snapshot_packager_service.rs
	modified:   core/tests/bank_forks.rs
	modified:   ledger/src/snapshot_package.rs
	modified:   runtime/src/bank.rs

Unmerged paths:
  (use "git add <file>..." to mark resolution)

	both modified:   ledger/src/snapshot_utils.rs

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[ryoqun]

oah, this is rather desired to be backported for the upcoming fix #8168

[codecov]

Codecov Report

Merging #8320 into v0.23 will not change coverage.
The diff coverage is 20%.

@@          Coverage Diff          @@
##           v0.23   #8320   +/-   ##
=====================================
  Coverage   80.8%   80.8%           
=====================================
  Files        251     251           
  Lines      54820   54820           
=====================================
  Hits       44333   44333           
  Misses     10487   10487