Expect metric only as a generic argument in logical meter formulas

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[shsms]

Based on #30

[Copilot]

Pull request overview

This PR updates the logical meter API to treat the selected metric purely as a type-level choice (generic parameter) rather than a runtime value, and refactors formula plumbing accordingly.

Changes:

• Updated LogicalMeterHandle formula streaming methods to take the metric via a generic type argument (removing the metric value parameter).
• Refactored formula construction to stop carrying metric instances (using PhantomData and associated constants instead).
• Updated tests, examples, and release notes to match the new call syntax.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
src/metric.rs	Adjusts the Metric trait and metric definitions to support type-only usage (adds str_name(), removes Display impls).
src/logical_meter/logical_meter_handle.rs	Changes public handle methods to use metric as a generic argument and updates call sites in tests.
src/logical_meter/formula/graph_formula_provider.rs	Removes runtime metric parameters from graph formula provider APIs; updates error message formatting.
src/logical_meter/formula/coalesce_formula.rs	Removes stored metric value from formula structs and uses PhantomData.
src/logical_meter/formula/aggregation_formula.rs	Removes stored metric value from formula structs and uses PhantomData.
src/logical_meter/formula.rs	Updates FormulaParams to no longer store a metric value (uses PhantomData).
RELEASE_NOTES.md	Documents the new LogicalMeterHandle call syntax (needs wording + additional breaking-change notes).
examples/logical_meter.rs	Updates example usage to the new turbofish syntax.

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