Add max cursors per txn check in KV Tx RPC

[canepat]

This PR introduces a sanity check on max number of opened cursors per txn in KV Tx RPC.

[codecov]

Codecov Report

Merging #645 (e5eeccf) into master (536cde7) will increase coverage by 0.30%.
The diff coverage is 75.00%.

@@            Coverage Diff             @@
##           master     #645      +/-   ##
==========================================
+ Coverage   82.53%   82.84%   +0.30%     
==========================================
  Files         176      176              
  Lines       15239    15257      +18     
==========================================
+ Hits        12578    12639      +61     
+ Misses       2661     2618      -43     

Impacted Files	Coverage Δ
node/silkworm/rpc/kv_calls.cpp	94.87% <75.00%> (+7.48%)	⬆️
core/silkworm/execution/evm.cpp	95.27% <0.00%> (-0.83%)	⬇️
core/silkworm/trie/hash_builder.cpp	99.29% <0.00%> (-0.71%)	⬇️
core/silkworm/state/intra_block_state.cpp	97.46% <0.00%> (+0.94%)	⬆️
node/silkworm/rpc/server_config.cpp	100.00% <0.00%> (+27.27%)	⬆️

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