Fix state sync halt issue

[yzang2019]

Describe your changes and provide context

The issue is that when a node is exporting snapshot for wasm, it needs to reopen the SC store for a given height, which could take 10-20 minutes, during that time, we acquired a lock which blocks the block commit.

The fix is to fix the lock usage to only apply after we open the DB.

Testing performed to validate your change

Tested on state sync node

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 5 lines in your changes missing coverage. Please review.

Project coverage is 54.86%. Comparing base (2815ef1) to head (85752e9).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
storev2/rootmulti/store.go	0.00%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #559      +/-   ##
==========================================
- Coverage   54.87%   54.86%   -0.01%     
==========================================
  Files         631      631              
  Lines       54946    54946              
==========================================
- Hits        30149    30145       -4     
- Misses      22641    22644       +3     
- Partials     2156     2157       +1     

Files with missing lines	Coverage Δ
storev2/rootmulti/store.go	2.56% <0.00%> (ø)

... and 2 files with indirect coverage changes