fix: restore OM1/protobuf micrometer suffix compatibility

[zeitlinger]

Fixes #2095

Summary

Restores OM1/protobuf compatibility for dotted gauge names after
feat: move suffix handling to scrape time (#1955).

The bug was that non-OpenMetrics exposition changed visible output for gauge
names that merely ended in suffix-like dotted strings such as .created and
.total.

Examples:

• Gauge("test3.created") regressed from test3 to test3_created
• Gauge("test6.total") regressed from test6 to test6_total

This PR restores the legacy OM1/protobuf behavior while keeping OpenMetrics on
literal-name handling.

What changed

• Fix OM1 text exposition for dotted gauge names ending in .created and
  .total
• Fix protobuf exposition for the same compatibility cases
• Add regression tests that cover the restored OM1/protobuf behavior and the
  preserved OpenMetrics behavior
• Add downstream Micrometer compatibility tasks and workflow so this class of
  regression is exercised automatically against Micrometer
• Pin the downstream Micrometer target to an immutable commit SHA so PR CI is
  deterministic

Related Micrometer work

While debugging this, we also found a separate Micrometer adapter bug:
registration-time collision detection needed snapshot-derived
MultiCollector metadata.

That fix lives on the downstream Micrometer branch used by the compatibility
job. The Micrometer coverage added here is regression protection; the prom-side
bug fix in this PR is the OM1/protobuf suffix compatibility restoration.

Related

• Issue: bug: restore OM1/protobuf suffix compatibility after #1955 #2095

Test plan

• mise run build
• mise run lint
• ./mvnw test -pl prometheus-metrics-exposition-textformats,prometheus-metrics-exposition-formats -Dtest=ExpositionFormatsTest,ProtobufExpositionFormatsTest -Dcoverage.skip=true -Dcheckstyle.skip=true
• GRADLE_USER_HOME=/tmp/gradle-micro ./gradlew --no-daemon -I /tmp/micrometer-prom-local.init.gradle :micrometer-registry-prometheus:test --tests io.micrometer.prometheusmetrics.PrometheusMeterRegistryTest
• GRADLE_USER_HOME=/tmp/gradle-micro ./gradlew --no-daemon -I /tmp/micrometer-prom-local.init.gradle :micrometer-registry-prometheus:test

[zeitlinger]

don't merge that!

[zeitlinger]

Superseded by a split PR stack so the prom-side fix can merge independently:

• upstream fix PR: fix: restore legacy suffix compatibility #2100
• stacked micrometer workflow PR: feat: add micrometer compatibility workflow zeitlinger/client_java#1

Closing this combined PR in favor of those two replacements.

[zeitlinger]

Closing in favor of #2100 plus the stacked Micrometer follow-up at zeitlinger#1.