Do not return an error when block is unavailable due to expiry

[turbolent]

Closes #5852

#5607 broke the getBlock function in Cadence.

When a block is not available, indicate it via the exists return value, but do not return an error.

blockInfo had no tests, which is why #5607 silently broke the getBlock function.

This PR fixes the bug and adds a test for blockInfo.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 33.33333% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 55.52%. Comparing base (b8c5da5) to head (3ba3a7e).
Report is 846 commits behind head on master.

Files	Patch %	Lines
utils/unittest/fixtures.go	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5853      +/-   ##
==========================================
+ Coverage   55.41%   55.52%   +0.10%     
==========================================
  Files        1108     1132      +24     
  Lines       86565    89476    +2911     
==========================================
+ Hits        47970    49679    +1709     
- Misses      33958    35021    +1063     
- Partials     4637     4776     +139     

Flag	Coverage Δ
unittests	55.52% <33.33%> (+0.10%)	⬆️

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[zhangchiqing]

Thanks for the fix.

[turbolent]

Thanks for the test @zhangchiqing!