Use dependency inversion to remove handler delayed import in eval_expr

[r41k0u]

Fixes #49

[Copilot]

Pull Request Overview

This PR removes a circular dependency issue by implementing dependency inversion to eliminate the delayed import of helper handlers in the expression evaluator. The change introduces a registry pattern that allows the helper module to register its handler with the expression module, rather than the expression module directly importing from the helper module.

• Introduced a CallHandlerRegistry class in the expression module to manage call handlers
• Moved helper call handling logic from eval_expr to a registration function in the helper module
• Replaced delayed imports and direct helper handling with registry-based delegation

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
pythonbpf/helper/init.py	Added registration function that sets up helper call handler with the expression module registry
pythonbpf/expr/expr_pass.py	Added CallHandlerRegistry class and simplified eval_expr to use registry delegation
pythonbpf/expr/init.py	Exported CallHandlerRegistry to make it available for registration

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