[EVM] Extend random source size

[devbugging]

Closes: #6165

Extend random source to return 32 bytes instead of 8.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 33.33333% with 6 lines in your changes missing coverage. Please review.

Project coverage is 41.66%. Comparing base (ab87266) to head (30b5831).

Files	Patch %	Lines
fvm/evm/handler/precompiles.go	16.66%	4 Missing and 1 partial :warning:
fvm/environment/history_random_source_provider.go	0.00%	1 Missing :warning:

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #6169   +/-   ##
=======================================
  Coverage   41.65%   41.66%           
=======================================
  Files        1975     1975           
  Lines      139640   139640           
=======================================
+ Hits        58172    58184   +12     
+ Misses      75430    75421    -9     
+ Partials     6038     6035    -3     

Flag	Coverage Δ
unittests	41.66% <33.33%> (+<0.01%)	:arrow_up:

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