feat(audit): add internal audit API client

[nycomp]

Overview

Adds an internal HTTP client for the Campus audit service that follows Campus API schema conventions. This client enables campus.auth and campus.api deployments to send trace spans to campus.audit via HTTP.

Changes

Client Implementation

• campus/audit/client/__init__.py - AuditClient entry point with environment-based URL resolution
• campus/audit/client/interface.py - ResourceRoot, ResourceCollection, Resource base classes
• campus/audit/client/v1/__init__.py - v1 API module
• campus/audit/client/v1/root.py - AuditRoot resource
• campus/audit/client/v1/traces.py - Traces, Trace, Spans, Span resources with nested class structure

Unit Tests

• tests/unit/audit/test_client.py - Client initialization tests
• tests/unit/audit/test_interface.py - Base resource class tests
• tests/unit/audit/test_traces.py - Traces resource tests

API Usage

from campus.audit.client import AuditClient

client = AuditClient()

# Ingest spans
client.traces.new(span_data)           # Single
client.traces.new(s1, s2, s3)          # Batch

# List/search traces
client.traces.list(limit=10)
client.traces.search(path="/api/v1/users")

# Get trace tree
tree = client.traces[trace_id].get_tree()

# Get span
span = client.traces[trace_id].spans[span_id].get()

Design

Follows campus-api-python structure with:

• ResourceCollection for collections
• Nested classes for individual items
• Standard verbs: new(), list(), search(), get()
• Bracket access for IDs: client.traces[trace_id]
• Property access for named sub-resources: client.traces[trace_id].spans

Related Issues

• Resolves Internal Audit API Client for Service-to-Service Communication #453
• Part of: Audit Phase 4: Tracing Middleware #428 (Phase 4: Tracing Middleware)