Implements send and target expressions

[johnnyt]

Adds comprehensive expression compilation during document validation and makes all actions pipeline-friendly for better Elixir ergonomics.

Expression Compilation Improvements

• Moves compilation to validation phase: All expressions (transitions, actions) are now compiled during document validation rather than at creation time
• Adds ExpressionCompiler module: Centralized compilation logic with detailed warning collection and source location tracking
• Supports all action types: SendAction, AssignAction, IfAction, ForeachAction with compiled expression fields
• Provides runtime fallbacks: Maintains backward compatibility with runtime compilation when validation-time compilation is unavailable
• Collects compilation warnings: Detailed error context with line/column information for debugging

Pipeline-Friendly Architecture

• Reorders function arguments: All action execute functions now take state_chart as the first argument
• Enables pipeline composition: Actions can now be chained idiomatically with the |> operator
• Updates ActionExecutor: All action calls updated to match new argument order
• Maintains compatibility: Function clauses ensure type safety with new signature

Code Quality Improvements

• Resolves Credo issues: Reduces cyclomatic complexity and fixes naming consistency
• Improves maintainability: Cleaner abstractions and better separation of concerns
• Comprehensive test coverage: All changes covered with updated test suites (112 action tests pass)

Performance Benefits

• Pre-compiled expressions: Significant performance improvement by compiling expressions once during validation
• Optimized evaluation: Expressions are compiled with Predicator once rather than on every execution
• Better error handling: Compilation errors are caught early with detailed warnings

Example Usage

# Pipeline-friendly action execution
state_chart
|> AssignAction.execute(assign_action)
|> LogAction.execute(log_action)
|> SendAction.execute(send_action)

# Expressions compiled during validation with warnings
{warnings, compiled_document} = ExpressionCompiler.compile_document(document)

[codecov]

Codecov Report

❌ Patch coverage is 87.37864% with 13 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
lib/statifier/actions/send_action.ex	75.00%	6 Missing ⚠️
lib/statifier/actions/action_executor.ex	66.66%	3 Missing ⚠️
lib/statifier/actions/if_action.ex	62.50%	3 Missing ⚠️
lib/statifier/validator/expression_compiler.ex	98.24%	1 Missing ⚠️

Files with missing lines	Coverage Δ
lib/statifier/actions/assign_action.ex	100.00% <ø> (+7.14%)	⬆️
lib/statifier/actions/foreach_action.ex	93.87% <ø> (-0.47%)	⬇️
lib/statifier/actions/log_action.ex	83.33% <ø> (ø)
lib/statifier/actions/raise_action.ex	100.00% <ø> (ø)
lib/statifier/feature_detector.ex	94.02% <ø> (ø)
lib/statifier/parser/scxml/element_builder.ex	100.00% <ø> (ø)
lib/statifier/validator.ex	100.00% <100.00%> (ø)
lib/statifier/validator/expression_compiler.ex	98.24% <98.24%> (ø)
lib/statifier/actions/action_executor.ex	68.33% <66.66%> (-0.52%)	⬇️
lib/statifier/actions/if_action.ex	77.77% <62.50%> (-11.12%)	⬇️
... and 1 more

... and 1 file with indirect coverage changes

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