feat[venom]: add assert combiner optimization pass

[harkal]

What I did

Add a new Venom optimization pass that combines adjacent assert iszero(x) sequences into a single assert using or, reducing bytecode size and gas cost.

How I did it

The implementation is split into two phases per reviewer request:

• Analysis phase (_AssertCombineAnalysis): identifies pairs of asserts that can be merged based on compatible error messages and no side-effecting instructions between them
• Transformation phase (AssertCombinerPass): applies the merges, combining predicates with or and removing redundant asserts

Key features:

• Preserves error message matching (only merges asserts with same error_msg)
• Respects side-effect barriers (mstore, sstore, mload, sload break chains)
• Handles chained merges (3+ consecutive asserts merge into one)
• Follows assign chains to find underlying iszero operations
• Removes duplicate asserts on the same predicate

How to verify it

Run the unit tests:

pytest tests/unit/compiler/venom/test_assert_combiner.py -v

Commit message

feat[venom]: add assert combiner optimization pass

This pass combines adjacent `assert iszero(x)` sequences into a single
assert using `or`, reducing bytecode size and gas cost.

The implementation is split into two phases:
- Analysis phase (`_AssertCombineAnalysis`): identifies pairs of asserts
  that can be merged based on compatible error messages and no side-
  effecting instructions between them
- Transformation phase (`AssertCombinerPass`): applies the merges,
  combining predicates with `or` and removing redundant asserts

Key features:
- Preserves error message matching (only merges asserts with same
  error_msg)
- Respects side-effect barriers (mstore, sstore, mload, sload break
  chains)
- Handles chained merges (3+ consecutive asserts merge into one)
- Follows assign chains to find underlying iszero operations
- Removes duplicate asserts on the same predicate

Description for the changelog

Add AssertCombinerPass optimization that combines adjacent assert conditions using bitwise OR.

Cute Animal Picture

[codecov]

Codecov Report

❌ Patch coverage is 88.18182% with 13 lines in your changes missing coverage. Please review.
✅ Project coverage is 93.32%. Comparing base (688aa54) to head (9e4e44b).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
vyper/venom/passes/assert_combiner.py	88.07%	6 Missing and 7 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4818      +/-   ##
==========================================
- Coverage   93.35%   93.32%   -0.03%     
==========================================
  Files         148      149       +1     
  Lines       20588    20698     +110     
  Branches     3574     3599      +25     
==========================================
+ Hits        19220    19317      +97     
- Misses        917      923       +6     
- Partials      451      458       +7     

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[charles-cooper]

please split this into an analysis pass (can be a local _AssertCombineAnalysis) and code modification pass

[charles-cooper]

@codex do you work yet

[chatgpt-codex-connector]

Codex couldn't complete this request. Try again later.

[vyperteam-bot]

Addressed review comment: split into analysis phase (_AssertCombineAnalysis) and transformation phase. All tests pass.