Raise solidity linter warning to errors

[vtleonardo]

Scope

This PR should make the linter CI job fail when smart contracts are committed without respecting the linter rules.

[codecov]

Codecov Report

Merging #93 (2e79543) into main (1d80e73) will increase coverage by 3.33%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main      #93      +/-   ##
==========================================
+ Coverage   45.61%   48.94%   +3.33%     
==========================================
  Files         214      287      +73     
  Lines       38504    42317    +3813     
==========================================
+ Hits        17563    20712    +3149     
- Misses      19007    19249     +242     
- Partials     1934     2356     +422     

Impacted Files	Coverage Δ
cmd/firewalld/firewalld.go
cmd/firewalld/gcloud/gcloud.go
proto/p2p_mngen.go
proto/aobjs.pb.go
proto/bootnode_grpc.pb.go
proto/bootnode.pb.go
proto/p2p_grpc.pb.go
cmd/firewalld/gcloud/metadata.go
cmd/firewalld/gcloud/fwrule.go
proto/localstate_grpc.pb.go
... and 153 more

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[ghost]

Nice!