fix(share/availability): propagate errors from light availability properly

[walldiss]

• Fix ctx canceled error being returned before sampling result is persisted.
• Store Put error should be propagated to the caller, to allow retry of sampling for the same height.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 6 lines in your changes missing coverage. Please review.

Project coverage is 45.20%. Comparing base (2469e7a) to head (413ffdc).
Report is 364 commits behind head on main.

Files with missing lines	Patch %	Lines
share/availability/light/availability.go	0.00%	5 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3888      +/-   ##
==========================================
+ Coverage   44.83%   45.20%   +0.37%     
==========================================
  Files         265      310      +45     
  Lines       14620    21873    +7253     
==========================================
+ Hits         6555     9888    +3333     
- Misses       7313    10924    +3611     
- Partials      752     1061     +309     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[renaynay]

agree w hlib re log, otherwise gtg