feat(compat): add Azure inventory payload core

[nina9753]

Summary

• add the reusable serverless compatibility inventory crate and payload builder
• collect canonical Azure Functions identity, slot, runtime, and subscription metadata
• keep scheduling and transport out of this foundational slice

Stack

1. feat(compat): add Azure inventory payload core #175 — Azure identity and core payload (this PR)
2. feat(compat): add GCP inventory collection #176 — GCP inventory collection, based on this PR
3. feat(compat): add serverless-compat inventory reporter (SVLS-9604) #161 — reporter, transport, and compat integration

#176 targets this PR branch. #161 will be rebuilt on #176 and retained as the top, end-to-end-testable PR so its existing URL, comments, and review history remain intact.

Testing

• cargo test --package datadog-serverless-compat-inventory --locked --offline
• cargo clippy --package datadog-serverless-compat-inventory --all-targets --locked --offline -- -D warnings
• rustfmt --edition 2024 --check on all new Rust sources
• git diff --check

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-29T13:48:55.941936Z	cd00914	PR opened

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[Copilot]

Copilot review overview

🟡 Changes recommended

Unsafe test environment mutation, missing override coverage, and the unrelated TLS downgrade should be addressed.

Review effort: Balanced
Findings: 1 · 1

Open (2)

• Unsafe environment access is not synchronized across tests · New
• Add tests for runtime handoff override precedence and fallback · New

What changed in this PR

Adds the foundational Azure Functions inventory payload crate for Serverless Compat.

Changes:

• Collects canonical Azure identity, slot, runtime, region, and subscription metadata.
• Builds serialized Fleet Automation inventory payloads.
• Adds focused Azure and payload tests.

File	Description
src/​platform/​mod.rs	Dispatches platform metadata collection.
src/​platform/​azure.rs	Collects Azure Functions metadata and identity.
src/​payload.rs	Constructs serialized inventory payloads.
src/​lib.rs	Exposes the inventory report API.
Cargo.toml	Defines the new crate and dependencies.
Cargo.lock	Registers the crate and changes rustls.

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[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: cd00914fa7

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[apiarian-datadog]

looks pretty good to me, tho i'd defer to folks more familiar with serverless compat for an ultimate review.