fix: Improve usage reporting

[jsonbailey]

Requirements

• I have added test coverage for new or changed functionality
• I have followed the repository's pull request submission guidelines
• I have validated my changes against all supported platform versions

Related issues

• Implements AIC-1636
• Spec: https://github.com/launchdarkly/sdk-specs/pull/132
• Context kind update: https://github.com/launchdarkly/sdk-specs/pull/134
• Naming consistency: https://github.com/launchdarkly/sdk-specs/pull/135
• JS reference implementation: fix: Improve usage reporting js-core#1108
• Python reference implementation: fix: Improve usage reporting python-server-sdk-ai#92

Describe the solution you've provided

Aligns the Ruby AI SDK's usage tracking with the updated spec from sdk-specs PRs #132, #134, and #135. Three categories of changes:

1. Renamed usage tracking event key from $ld:ai:config:function:single to $ld:ai:usage:completion-config, matching the new unified $ld:ai:usage:* namespace. (This SDK only has the single completion config method — no judge, agent, or createChat methods — so only one key needed updating.)

2. Added SDK info tracking on initialization ($ld:ai:sdk:info). When Client is constructed, it fires a single tracking event with SDK name, version, and language using an anonymous context with kind ld_ai and key ld-internal-tracking. SDK identity constants are kept in a dedicated sdk_info.rb module (similar to sdkInfo.ts in JS and sdk_info.py in Python).

3. Renamed config to completion_config to align with the updated spec method naming. The old config method is preserved as a deprecated proxy that emits a warning and delegates to completion_config.

Human review checklist

• Verify event key string $ld:ai:sdk:info uses colons (not dashes) per sdk-specs PR #135
• Verify event key string $ld:ai:usage:completion-config exactly matches the spec
• Verify the anonymous context uses kind ld_ai (underscore) with key ld-internal-tracking per sdk-specs PRs #134/#135
• Confirm that INIT_TRACK_CONTEXT being created at module load time (outside class Client) is acceptable — it calls LDContext.create when the module is first loaded
• Confirm the deprecation approach for config (emitting warn on every call) is acceptable for existing consumers

Additional context

• Link to Devin run: https://app.devin.ai/sessions/9c25c81dfcc347a08bdd5f168ae59725
• Requested by: @jsonbailey

[devin-ai-integration]

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

View in Devin Review to see 4 additional findings.

[jsonbailey]

Why is version required here?

[devin-ai-integration]

You're right, it's not needed here — sdk_info.rb doesn't reference VERSION. Removed.