refactor: Upgrade to Pydantic v2

[msbrogli]

Motivation

This PR upgrades the codebase from Pydantic v1 to Pydantic v2.

Acceptance Criteria

• Update pydantic dependency from ~1.10.26 to ^2.0 in pyproject.toml
• Migrate @validator decorators to @field_validator with mode='before'/mode='after' instead of pre=True
• Migrate cross-field validators to @model_validator(mode='after') pattern, replacing values dict access with direct model attribute access
• Replace Extra.ignore and other class-level config with model_config = ConfigDict(...)
• Replace .dict() calls with .model_dump()
• Update discriminated unions to use Discriminator() and Tag() from pydantic
• Remove deprecated allow_reuse=True and each_item=True parameters (handled differently in v2)
• Add @classmethod decorator to field validators as required by v2
• Add Hex[bytes] type annotation for automatic hex string parsing

Checklist

• If you are requesting a merge into master, confirm this code is production-ready and can be included in future releases as soon as it gets merged

[github-actions]

Bencher Report

Branch	refactor/pydantic-v2
Testbed	ubuntu-22.04

🚨 1 Alert

Benchmark	Measure Units	View	Benchmark Result (Result Δ%)	Lower Boundary (Limit %)
sync-v2 (up to 20000 blocks)	Latency minutes (m)	📈 plot 🚷 threshold 🚨 alert (🔔)	1.36 m (-20.56%) Baseline: 1.72 m	1.54 m (113.29%)

Click to view all benchmark results

Benchmark	Latency	Benchmark Result minutes (m) (Result Δ%)	Lower Boundary minutes (m) (Limit %)	Upper Boundary minutes (m) (Limit %)
sync-v2 (up to 20000 blocks)	📈 view plot 🚷 view threshold 🚨 view alert (🔔)	1.36 m (-20.56%) Baseline: 1.72 m	1.54 m (113.29%)	2.06 m (66.20%)

🐰 View full continuous benchmarking report in Bencher

[msbrogli]

I'd rather use exclude instead of update.

[msbrogli]

It seems exclude is not available in Pydantic v2. I guess it is ok to simply replace it by an empty dict.

[msbrogli]

Can it really be None?

[codecov]

Codecov Report

❌ Patch coverage is 95.96774% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.26%. Comparing base (a010288) to head (84527e6).

Files with missing lines	Patch %	Lines
hathor/consensus/poa/poa_signer.py	78.26%	2 Missing and 3 partials ⚠️
hathor/utils/named_tuple.py	75.00%	2 Missing and 1 partial ⚠️
hathor/utils/pydantic.py	90.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1566      +/-   ##
==========================================
- Coverage   86.33%   86.26%   -0.07%     
==========================================
  Files         437      437              
  Lines       33645    33610      -35     
  Branches     5258     5259       +1     
==========================================
- Hits        29047    28994      -53     
- Misses       3594     3606      +12     
- Partials     1004     1010       +6     

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[msbrogli]

Pydantic v2 requires default value to ignore missing parameters. Should these None be included?