feat: Upgrade to adcp-client-python 2.18.0 and enhance list_creative_formats response

[BaiyuScope3]

Summary

This PR upgrades the adcp-client-python dependency to 2.18.0 and enhances the list_creative_formats tool to provide better human-readable output for LLM consumption.

Changes

1. Enhanced list_creative_formats Response

Added human-readable format details in the tool response content field
Each format now displays: name, ID, type, dimensions, description, required assets, optional assets, and supported macros
LLMs can now see full format specifications without needing structured data parsing

2. Upgraded to adcp-client-python 2.18.0

Updated dependency from adcp>=2.13.0 to adcp>=2.18.0
Migrated to new assets field (replaces deprecated assets_required)
Added create_asset() helper function returning the new Assets type
Backfill assets_required from assets for backward compatibility using get_required_assets() utility

3. Added Optional Impression Tracker Asset

Added create_impression_tracker_asset() helper for 3rd party tracking pixels
All formats (except VAST) now include an optional impression_tracker asset
VAST formats excluded as they have built-in tracking in the XML

4. Updated Server Utilities

_format_to_human_readable() now uses get_required_assets() and get_optional_assets() from adcp
Properly distinguishes between required and optional assets in output

5. Test Updates

Updated tests for PreviewRender which is now a RootModel (access via .root)
Updated tests for relaxed schema validation (additional fields now allowed)
Updated test_info_card_formats.py to verify new assets/assets_required structure

6. Bug Fix

Removed IMPRESSION_URL from COMMON_MACROS (not a universal macro)

Testing

All 256 tests pass ✅
Lint checks pass ✅

1. Test new assets discovery

2. Test improvement on LLM response

Before:

Now:

[BaiyuScope3]

IMPRESSION_URL is not part of adcp universal macro

[BaiyuScope3]

for backward compatibility, still populate assets_required fields extract from assets

[BaiyuScope3]

Impression Tracker Support by Format

Format ID	Type	Impression Tracker
display_generative	display	✅
display_300x250_generative	display	✅
display_728x90_generative	display	✅
display_320x50_generative	display	✅
display_160x600_generative	display	✅
display_336x280_generative	display	✅
display_300x600_generative	display	✅
display_970x250_generative	display	✅
display_image	display	✅
display_300x250_image	display	✅
display_728x90_image	display	✅
display_320x50_image	display	✅
display_160x600_image	display	✅
display_336x280_image	display	✅
display_300x600_image	display	✅
display_970x250_image	display	✅
display_html	display	✅
display_300x250_html	display	✅
display_728x90_html	display	✅
display_160x600_html	display	✅
display_336x280_html	display	✅
display_300x600_html	display	✅
display_970x250_html	display	✅
display_js	display	✅
video_standard	video	✅
video_dimensions	video	✅
video_standard_30s	video	✅
video_standard_15s	video	✅
video_1920x1080	video	✅
video_1280x720	video	✅
video_1080x1920	video	✅
video_1080x1080	video	✅
video_ctv_preroll_30s	video	✅
video_ctv_midroll_30s	video	✅
video_vast	video	❌
video_vast_30s	video	❌
native_standard	native	✅
native_content	native	✅
audio_standard_15s	audio	✅
audio_standard_30s	audio	✅
audio_standard_60s	audio	✅
dooh_billboard_1920x1080	dooh	✅
dooh_billboard_landscape	dooh	✅
dooh_billboard_portrait	dooh	✅
dooh_transit_screen	dooh	✅
product_card_standard	display	✅
product_card_detailed	display	✅
format_card_standard	display	✅
format_card_detailed	display	✅

Summary:** 47/49 formats support optional impression_tracker. VAST formats excluded (built-in tracking).