Fix View instrument-name matching to be case-insensitive and platform-independent

[winklemad]

Description

A View built with an instrument's real, documented name silently fails to match, so its aggregation / drop / rename / attribute filter is never applied.

Instrument names are valid mixed-case (the API name regex is [a-zA-Z][-_./a-zA-Z0-9]{0,254}), but the SDK lower-cases them on construction (_Synchronous/_Asynchronous set self.name = name.lower()). View._match compared the user's instrument_name pattern against that lower-cased name with fnmatch without lower-casing the pattern:

from opentelemetry.sdk.metrics import MeterProvider
from opentelemetry.sdk.metrics.view import View, DropAggregation
from opentelemetry.sdk.metrics.export import InMemoryMetricReader

reader = InMemoryMetricReader()
mp = MeterProvider(metric_readers=[reader],
    views=[View(instrument_name="MyLatency", aggregation=DropAggregation())])
mp.get_meter("m").create_counter("MyLatency").add(5)
# before: the counter is still exported (view did NOT match "mylatency")
# after:  the counter is dropped (view matches)

There's a second problem at the same spot: fnmatch applies os.path.normcase, which lower-cases on Windows but is identity on POSIX — so the same View matches on Windows and not on Linux/macOS.

Fix

Lower-case the name pattern (matching the SDK's own lower-casing, so names match case-insensitively as the duplicate-instrument-name check at #2409 already assumes), and use fnmatchcase for both the name and unit sites so matching no longer depends on the host platform. Units stay case-sensitive (per UCUM).

Test

Added test_instrument_name_case_insensitive and test_instrument_unit_case_sensitive to test_view.py; they fail on the previous code and pass with the fix. test_view.py → 11 passed.

Disclosure: this change was written with AI assistance (noted via an Assisted-by: commit trailer, per the project's guidance); I've reviewed and verified every line and the reproduction.

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: winklemad / name: winklemad (64d11a0)

[github-actions]

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[lzchen]

@winklemad

Please add a CHANGELOG entry.