feat(rust): accept the global meter provider without a wrapper type

[yordis]

• Consumers that hold the global meter provider only have a trait object, so they had to write a forwarding wrapper type just to construct a handle.
• Removing that friction lets applications adopt the generated handles with whatever provider they already have.

[cursor]

PR Summary

Low Risk
This widens constructor generics only; existing concrete-provider call sites should keep compiling, with no telemetry pipeline or security behavior changes.

Overview
Generated Meter, Tracer, and Logger new methods now take unsized OpenTelemetry providers (?Sized), so callers can pass trait objects such as &*opentelemetry::global::meter_provider() without a forwarding wrapper type.

The Rust template README documents that pattern with a global meter example. A metrics test asserts that a meter built from the global provider still exports the expected instrumentation scope and metric name. Weaver snapshot fixtures for generated handle modules were updated to match the new signatures.

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• templates/code/rust/README.md

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Reviewing files that changed from the base of the PR and between baafc32 and 78cf29b.

📒 Files selected for processing: 26

• templates/code/rust/README.md
• templates/code/rust/logger.rs.j2
• templates/code/rust/meter.rs.j2
• templates/code/rust/tests/allocations/expected/logger.rs
• templates/code/rust/tests/allocations/expected/meter.rs
• templates/code/rust/tests/event_no_attributes/expected/logger.rs
• templates/code/rust/tests/events/expected/logger.rs
• templates/code/rust/tests/histogram_boundaries_by_unit/expected/meter.rs
• templates/code/rust/tests/histogram_boundaries_by_unit_params/expected/meter.rs
• templates/code/rust/tests/imported/expected/logger.rs
• templates/code/rust/tests/imported/expected/meter.rs
• templates/code/rust/tests/imported/expected/tracer.rs
• templates/code/rust/tests/imported_typed/expected/logger.rs
• templates/code/rust/tests/imported_typed/expected/meter.rs
• templates/code/rust/tests/imported_typed/expected/tracer.rs
• templates/code/rust/tests/literal_escaping/expected/meter.rs
• templates/code/rust/tests/metrics/expected/meter.rs
• templates/code/rust/tests/metrics/test.rs
• templates/code/rust/tests/naming/expected/meter.rs
• templates/code/rust/tests/no_namespace/expected/logger.rs
• templates/code/rust/tests/no_namespace/expected/tracer.rs
• templates/code/rust/tests/params/expected/logger.rs
• templates/code/rust/tests/params/expected/meter.rs
• templates/code/rust/tests/params/expected/tracer.rs
• templates/code/rust/tests/spans/expected/tracer.rs
• templates/code/rust/tracer.rs.j2

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Walkthrough

Rust meter, logger, and tracer constructors now accept potentially unsized provider types. Generated outputs reflect the updated signatures. Documentation and a test demonstrate constructing a generated meter from the global meter provider.

Changes

Rust provider support

Layer / File(s)	Summary
Allow unsized provider types templates/code/rust/{logger,meter,tracer}.rs.j2, templates/code/rust/tests/*/expected/{logger,meter,tracer}.rs	The constructors add ?Sized to their provider bounds. Expected generated outputs use the updated signatures.
Document and test global-provider meter use templates/code/rust/README.md, templates/code/rust/tests/metrics/test.rs	The README shows constructing a generated meter from the global provider. The test constructs one from a global provider trait object, records MyappTaskStarted, and checks exported scope, schema URL, and metric name.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Feature

Merge Risk: ⚪ Minimal · up to 78cf2

Generated Rust constructors now accept the global meter provider trait object without a wrapper type. The change is backward compatible, and the README and test cover the new use. Merge risk is minimal.

Pre-merge checks: 4 · 1

Failed checks: 1 warning

Check name	Status	Explanation	Resolution
Docstring Coverage		Docstring coverage is 8.70% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 23 functions across 22 files. (4 skipped: …	Write docstrings for the functions missing them to satisfy the coverage threshold.

Passed checks: 4 passed

Check name	Status	Explanation
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.
Title check		The title clearly summarizes the main change: Rust handles can accept the global meter provider without a wrapper type.
Description check		The description directly explains why the change is needed and how it helps consumers use existing global meter provider trait objects.

Full details: Docstring Coverage

Explanation

Docstring coverage is 8.70% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 23 functions across 22 files. (4 skipped: 4 unsupported.)

✨ Finishing Touches: 💡 2

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_{I’m a rabbit with a meter to try,
I gather a task and let its notes fly.
Providers unsized can join in the run,
Their metrics are checked when the flush is done.
I nibble a clover and hop by the stream.}

_{Comment @coderabbitai help to get the list of available commands.}