Add solver method template

[ohno]

Summary

• add a minimal source template for new solver methods and result types
• show the expected solve and expectation dispatch points
• keep optional display and verification hooks separate from calculations
• condense the surrounding integration steps to avoid repeated guidance

Validation

• complete Documenter build passed with doctests, cross-references, and document checks
• git diff --check

Closes #14

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This pull request was developed with assistance from Codex using GPT-5.6 Sol with High reasoning effort.