Downloader printable peer-id

[mriccobene]

Erigon Sentry now uses pubkey as peer-id but pubkey has not printable characters. This PR use Bytes in place of string to represent peer-id and use hex encoding to print peer-id.

[codecov[bot]]

Codecov Report

Merging #748 (6a8cd19) into master (9004e9c) will decrease coverage by 0.19%. The diff coverage is 57.14%.

@@            Coverage Diff             @@
##           master     #748      +/-   ##
==========================================
- Coverage   76.31%   76.12%   -0.20%     
==========================================
  Files         190      190              
  Lines       13057    13060       +3     
  Branches     2119     2119              
==========================================
- Hits         9965     9942      -23     
- Misses       2212     2223      +11     
- Partials      880      895      +15     

Impacted Files	Coverage Δ
node/silkworm/downloader/internals/types.hpp	27.58% <0.00%> (-3.19%)	:arrow_down:
...ilkworm/downloader/internals/sentry_type_casts.cpp	96.29% <100.00%> (ø)
node/silkworm/rpc/server/call.hpp	70.00% <0.00%> (-2.58%)	:arrow_down:
node/silkworm/rpc/server/server_context_pool.cpp	62.60% <0.00%> (-1.63%)	:arrow_down:
core/silkworm/state/intra_block_state.cpp	94.01% <0.00%> (-1.41%)	:arrow_down:
core/silkworm/state/in_memory_state.cpp	91.66% <0.00%> (-1.05%)	:arrow_down:
core/silkworm/execution/evm.cpp	93.38% <0.00%> (-0.71%)	:arrow_down:
core/silkworm/types/block.cpp	87.00% <0.00%> (-0.50%)	:arrow_down:
core/silkworm/trie/hash_builder.cpp	98.13% <0.00%> (-0.47%)	:arrow_down:
core/silkworm/types/transaction.cpp	81.78% <0.00%> (-0.32%)	:arrow_down:

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