python(feat): report templates API resource

[wei-qlu]

Summary

Adds a report template API to sift_client:

template = client.reports.templates.create({"name": "Motor Checkout", "rule_ids": [r.id_ for r in rules]})
job = template.create_report(run=run)  # or client.reports.create_from_template(...); objects or IDs

• New client.reports.templates (sync and async) with get (by ID or client key), list_, find, create, update, archive, unarchive
• New ReportTemplate, ReportTemplateRule, ReportTemplateCreate, ReportTemplateUpdate types.
  • Templates reference existing rules: attach them by rule ID (rule_ids, also accepts Rule objects) or by rule client key (rule_client_keys), one scheme per request (validated client-side); templates return rules sorted by display_order
  • ReportTemplate.create_report(run=...) creates a report from the template in one call
• New ReportTemplatesLowLevelClient wrapping ReportTemplateService
• generate_sync_api gains nested_resources support: nested APIs get a cached property on the sync class that wraps the async instance held by the parent, with correct type stubs
• Updated generated docs to order by source (definition order) rather than alphabetical
• Breaking: reports.create_from_template now takes report_template (a ReportTemplate or ID) and run (a Run or ID) instead of report_template_id/run_id, matching the other create_from_* methods (CHANGELOG updated)

Test plan

• Unit tests across the type, low-level, resource, and sync wrapper layers
• Manual QA: find an existing rule, create a template from it, get by ID and client key, list/find, update (rename, rule replace, tag clear), create a report from the template (object and ID forms), and archive/unarchive

[github-actions]

Python docs preview: https://sift-stack.github.io/sift/python/pr-672/

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