Jsonrpc fix race conditions

[ferranbt]

Description

This PR fixes two race conditions in jsonrpc and one mutex lock. You can check the commits for each specific change.

Changes include

• Bugfix (non-breaking change that solves an issue)
• Hotfix (change that solves an urgent issue, and requires immediate attention)
• New feature (non-breaking change that adds functionality)
• Breaking change (change that is not backwards-compatible and/or changes current functionality)

Breaking changes

Please complete this section if any breaking changes have been made, otherwise delete it

Checklist

• I have assigned this PR to myself
• I have added at least 1 reviewer
• I have added the relevant labels
• I have updated the official documentation
• I have added sufficient documentation in code

Testing

• I have tested this code with the official test suite
• I have tested this code manually

Manual tests

Please complete this section if you ran manual tests for this functionality, otherwise delete it

Documentation update

Please link the documentation update PR in this section if it's present, otherwise delete it

Additional comments

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[codecov]

Codecov Report

Merging #908 (f7a4aa6) into develop (62d5981) will decrease coverage by 0.02%.
The diff coverage is 94.87%.

@@             Coverage Diff             @@
##           develop     #908      +/-   ##
===========================================
- Coverage    52.80%   52.77%   -0.03%     
===========================================
  Files          128      129       +1     
  Lines        17148    17153       +5     
===========================================
- Hits          9055     9053       -2     
- Misses        7444     7453       +9     
+ Partials       649      647       -2     

Impacted Files	Coverage Δ
jsonrpc/filter_manager.go	77.57% <94.87%> (+0.17%)	⬆️
state/state.go	35.29% <0.00%> (-15.87%)	⬇️
state/immutable-trie/state.go	50.81% <0.00%> (-2.89%)	⬇️
state/txn.go	17.12% <0.00%> (-2.64%)	⬇️
syncer/client.go	61.79% <0.00%> (-1.42%)	⬇️
state/immutable-trie/snapshot.go	58.33% <0.00%> (ø)
state/executor.go	3.96% <0.00%> (+0.07%)	⬆️
state/immutable-trie/trie.go	61.44% <0.00%> (+0.20%)	⬆️
network/server_discovery.go	76.39% <0.00%> (+1.86%)	⬆️

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[vcastellm]

LGTM aside from the suggestions

[Stefan-Ethernal]

LGTM