feat: account serialization overhaul

[pugachAG]

Change Account to be enum and use different representations for serde and borsh ser/deser:

• SerdeAccount is introduced for serde to maintain backward and forward compatibility. Previously Account struct was directly annotated to support serde, we are opting out of this.
• BorshVersionedAccount is introduced for borsh serialization. Accounts in old format are serialized directly as AccountV1. Note that we continue serializing in old format when possible to avoid 16 bytes overhead of sentinel padding.

Account::SERIALIZATION_SENTINEL hack is preserved for borsh serialization as I could not find a better way to handle backward compatibility.

This is part of #12716, in a separate PR global contracts related fields will be added as part of Account.

[codecov]

Codecov Report

Attention: Patch coverage is 90.44586% with 15 lines in your changes missing coverage. Please review.

Project coverage is 70.46%. Comparing base (5b32984) to head (2fb8991).
Report is 9 commits behind head on master.

Files with missing lines	Patch %	Lines
core/primitives-core/src/account.rs	90.44%	11 Missing and 4 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #12794      +/-   ##
==========================================
- Coverage   70.53%   70.46%   -0.08%     
==========================================
  Files         846      847       +1     
  Lines      174904   175051     +147     
  Branches   174904   175051     +147     
==========================================
- Hits       123372   123341      -31     
- Misses      46282    46453     +171     
- Partials     5250     5257       +7     

Flag	Coverage Δ
backward-compatibility	0.16% <0.00%> (-0.01%)	⬇️
db-migration	0.16% <0.00%> (-0.01%)	⬇️
genesis-check	1.41% <26.36%> (+0.06%)	⬆️
linux	70.06% <76.43%> (+0.89%)	⬆️
linux-nightly	70.10% <90.44%> (-0.05%)	⬇️
pytests	1.70% <26.36%> (+0.05%)	⬆️
sanity-checks	1.52% <26.36%> (+0.06%)	⬆️
unittests	70.29% <90.44%> (-0.08%)	⬇️
upgradability	0.20% <0.00%> (-0.01%)	⬇️

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