feat: add agent graph tracker

[andrewklatzke]

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

Describe the solution you've provided

Implements the AIGraphTracker class to handle tracking events for agent graphs in the SDK.

Describe alternatives you've considered

This is the primary implementation of the tracker. It's broken into its own tracker rather than polluting the interface of the BaseTracker or AiConfigTracker since this is a separate entity that has its own interaction & metric patterns.

Additional context

This implements the following events to be tracked:

Edge-level metrics

$ld:ai:graph:redirect<{ sourceKey, redirectedTarget }>
$ld:ai:graph:handoff_success<{ sourceKey, targetKey }>
$ld:ai:graph:handoff_failure<{ sourceKey, targetKey }>

Node level metrics

$ld:ai:graph:node_invocation<{ graphKey, configKey }>
$ld:ai:graph:tool_call<{ graphKey, configKey, toolKey }>
<judge_metrics><{ graphKey, configKey }> (judge on a specific node)

Graph metrics

$ld:ai:graph:invocation_success
$ld:ai:graph:invocation_failure
$ld:ai:graph:latency (total latency of the entire graph invocation)
$ld:ai:graph:total_tokens (total token usage of the graph invocation)
$ld:ai:graph:path<{ graphKey, ...configKey }>
<judge_metrics><{ graphKey }> (judges on final output)

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Note

Medium Risk
Introduces new analytics/telemetry behavior and changes the agent_graph return object shape by attaching a tracker, which could affect consumers and increase event volume/cost if used incorrectly.

Overview
Adds a new AIGraphTracker that can emit graph-, node-, and edge-level LaunchDarkly events (invocation success/failure, latency, tokens, path, redirects/handoffs, tool calls, and judge metric scores).

LDAIClient.agent_graph() now builds a tracker from flag variation metadata and attaches it to every returned AgentGraphDefinition (including disabled/invalid graphs), and AgentGraphDefinition exposes it via get_tracker(); AIGraphTracker is also exported from ldai.__init__.

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[andrewklatzke]

Unused import here, not sure why it wasn't picked up in previous lint