Extend brand_manifest non-standard-path warning to inline-object branch

[bokelley]

Background

Surfaced during rebase of PR #686 (#683) on top of PR #685 (#684), and called out by ad-tech-protocol-expert review of #686.

After both PRs merge, the v2.5 → v3 brand_manifest adapter handles two input shapes:

1. URL string — gets the non-standard-path warning from fix(compat): warn when brand_manifest non-standard path is silently flattened to domain #686.
2. Inline BrandManifest object with optional url field — translated to brand.domain via extract_brand_domain(url), but the non-standard-path warning is NOT applied.

The same information loss occurs in both cases: a non-canonical path on the inline-object's url field will be silently flattened to the hostname, and v3 sellers' canonical /.well-known/brand.json fetch will likely 404.

Suggested fix

Extract the warning logic into a shared helper (e.g. warn_if_brand_manifest_path_lossy in src/adcp/compat/legacy/v2_5/_url.py alongside extract_brand_domain) and call it from both branches in both adapters.

This also addresses the duplication nit code-reviewer raised on #686 (warning logic copy-pasted across get_products.py and _media_buy_helpers.py).

Affected call sites

• src/adcp/compat/legacy/v2_5/get_products.py:adapt_request — inline-object branch
• src/adcp/compat/legacy/v2_5/_media_buy_helpers.py:adapt_brand_manifest_to_brand — inline-object branch

Out of scope

Bounded dedup cache (_brand_manifest_path_warned is currently an unbounded set) — separate follow-up worth filing if production cardinality ever becomes a concern.