Add metrics to measure size of ChunkStateWitness fields

[jancionear]

Add metrics to measure the size of:

• ChunkStateWitness::main_state_transition
• ChunkStateWitness::new_transactions
• ChunkStateWitness::new_transactions_validation_state
• ChunkStateWitness::source_receipt_proofs

The new metrics look like this in Grafana:

They can be viewed here: https://nearone.grafana.net/d/edbl9ztm5h1q8b/stateless-validation?orgId=1&from=1714476360000&to=1714476660000&var-chain_id=mainnet&var-shard_id=All&var-node_id=jan-mainnet-node

Those metrics will help to estimate the proper limits for various fields of ChunKStateWitness

Refs: #11103

[jancionear]

I was worried that serializing the fields might take a long time, but on mainnet traffic record_witness_size_metrics() usually takes < 0.2ms to execute, with rare outliers up to 0.5ms, sometimes even 1ms.
I don't see an easy way to make it more efficient, so I'd say that it's acceptable, we can optimize it later if it turns up in profiling.

[codecov]

Codecov Report

Attention: Patch coverage is 89.32039% with 11 lines in your changes are missing coverage. Please review.

Project coverage is 71.16%. Comparing base (549f4b5) to head (dc93d05).
Report is 5 commits behind head on master.

Files	Patch %	Lines
chain/client/src/metrics.rs	93.81%	1 Missing and 5 partials ⚠️
...client/src/stateless_validation/shadow_validate.rs	0.00%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #11182      +/-   ##
==========================================
+ Coverage   71.06%   71.16%   +0.09%     
==========================================
  Files         779      780       +1     
  Lines      154698   155040     +342     
  Branches   154698   155040     +342     
==========================================
+ Hits       109938   110332     +394     
+ Misses      40353    40275      -78     
- Partials     4407     4433      +26     

Flag	Coverage Δ
backward-compatibility	0.24% <0.00%> (-0.01%)	⬇️
db-migration	0.24% <0.00%> (-0.01%)	⬇️
genesis-check	1.41% <0.00%> (-0.01%)	⬇️
integration-tests	37.15% <89.32%> (+0.15%)	⬆️
linux	69.28% <0.00%> (-0.13%)	⬇️
linux-nightly	70.59% <89.32%> (+0.06%)	⬆️
macos	52.98% <0.00%> (-0.20%)	⬇️
pytests	1.64% <0.00%> (-0.01%)	⬇️
sanity-checks	1.43% <0.00%> (-0.01%)	⬇️
unittests	65.75% <88.34%> (-0.02%)	⬇️
upgradability	0.29% <0.00%> (-0.01%)	⬇️

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