CLI startup optimization: lazy import heavy modules in exstruct.cli.main

[harumiWeb]

Before submitting

• I understand that this project is maintained in spare time and that not all issues may result in changes.

Description

Summary

The current CLI entrypoint imports extraction-related code such as process_excel and edit CLI modules at module import time.
As a result, even lightweight commands like exstruct --help or exstruct ops list pay the import cost of heavier extraction-related dependencies.

To reduce startup latency, we should minimize top-level imports in the CLI entrypoint and import implementation modules only after command routing is known.

Problem

The current structure front-loads import cost for:

• extraction APIs
• edit CLI implementations
• their transitive heavy dependencies

This creates avoidable inefficiencies:

• --help is slower than it should be
• edit commands pay extraction import cost
• extraction commands may also import edit-related code unnecessarily

Proposal

• Keep src/exstruct/cli/main.py top-level imports as light as possible
• Route commands based on argv before importing heavy modules
• Import exstruct.cli.edit only when edit commands are invoked
• Import process_excel only immediately before extraction execution

The guiding principle is:

• CLI startup should only do lightweight routing
• Implementation code should be imported only when needed

Expected benefits

• Faster startup for exstruct --help
• Faster startup for lightweight edit commands such as exstruct ops list
• Cleaner separation of CLI responsibilities
• Easier measurement and reasoning using -X importtime

Scope

Potential files:

• src/exstruct/cli/main.py
• possibly src/exstruct/cli/edit.py

Acceptance criteria

• exstruct --help does not require extraction-related heavy imports
• exstruct ops list does not require importing process_excel
• process_excel is imported only when extraction execution begins
• Existing CLI behavior remains backward-compatible

Notes

This is likely a relatively low-risk change and a strong first step for improving startup latency.

Minimal example (optional)

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Additional notes (optional)

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