feat(store): allow partial init

[Wondertan]

Previously, if either head or tail is not found for whatever reason, the store will report being empty, causing the node to reinitialize and sync from scratch. This change enables it to recover either the head or the tail if the other is missing. For example, if the tail is missing due to an interrupted delete, the head will be retrieved successfully upon start. The tail will then be recovered via the receding tail functionality. Although if the chain is too long, receding may take too long making it hard for the node to stop, thus #326

This was tested manually, but it still needs a unit test. It will happen in a separate PR

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 71.42857% with 8 lines in your changes missing coverage. Please review.

Project coverage is 53.93%. Comparing base (88c5b8c) to head (854b811).
Report is 76 commits behind head on main.

Files with missing lines	Patch %	Lines
store/store.go	71.42%	5 Missing and 3 partials ⚠️

❗ There is a different number of reports uploaded between BASE (88c5b8c) and HEAD (854b811). Click for more details.

HEAD has 1 upload less than BASE

Flag	BASE (88c5b8c)	HEAD (854b811)
	2	1

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #327      +/-   ##
==========================================
- Coverage   62.80%   53.93%   -8.88%     
==========================================
  Files          39       39              
  Lines        3589     4439     +850     
==========================================
+ Hits         2254     2394     +140     
- Misses       1160     1864     +704     
- Partials      175      181       +6     

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