vmgs: Write a diagnostic marker when provisioning the VMGS

[stunes-ms]

We want to leave a marker in a VMGS file that indicates that it was provisioned originally by HCL, with some diagnostic details (vTPM version, etc.) This is intended to be information-only: the marker is written once when a new VMGS file is provisioned by OpenHCL. It causes no functional changes, so OpenHCL does not need to read the marker when loading a VMGS file. Its purpose is to help us track down the origin of a VMGS file when debugging.

The marker is a JSON string containing parameters of interest from the initial creation of the VMGS file. Example (this is pretty-printed for readability; the actual marker is not):

{
"provisioner": "openhcl",
"reason": "empty",
"tpm_version": "1.38",
"tpm_nvram_size": 32768,
"akcert_size": 4096,
"akcert_attrs": "0x42060004",
"hcl_version": "f85a038845b4fd5c74726be38f4be690c99db8c6"
}

This adds dependencies on serde to vmgs_format (to make the VmgsProvisioningMarker struct serializable) and on serde_json to vmgs (to convert a VmgsProvisioningMarker to a string to write it to the VMGS file).

[Copilot]

Pull request overview

This PR adds diagnostic provisioning markers to VMGS (Virtual Machine Guest State) files to track when and how they were provisioned by OpenHCL, including details about the vTPM configuration.

Changes:

• Introduces a new vmgs_ext crate with types for tracking provisioning information (provisioner type, reason, TPM details)
• Refactors VMGS provisioning tracking from a boolean to an Option<VmgsProvisioningReason> to capture why provisioning occurred
• Extracts TPM-related constants and helper functions to improve code reusability
• Adds logic in OpenHCL to write a JSON-formatted provisioning marker when a VMGS file is newly provisioned

Reviewed changes

Copilot reviewed 12 out of 13 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
vm/vmgs/vmgs_ext/src/lib.rs	New crate defining provisioning marker types and enums
vm/vmgs/vmgs_ext/Cargo.toml	Cargo configuration for the new vmgs_ext crate
vm/vmgs/vmgs_format/src/lib.rs	Adds PROVISIONING_MARKER FileId (18) to the VMGS format
vm/vmgs/vmgs/src/vmgs_impl.rs	Refactors provisioning tracking to use VmgsProvisioningReason enum and adds provisioning_reason() method
vm/vmgs/vmgs/Cargo.toml	Adds vmgs_ext dependency
vm/devices/tpm/tpm_protocol/src/lib.rs	Extracts platform_akcert_attributes() helper and TPM default constants
vm/devices/tpm/tpm_protocol/src/tpm20proto.rs	Updates test to use extracted platform_akcert_attributes() helper
vm/devices/tpm/tpm_lib/src/lib.rs	Uses extracted constants and helper function instead of local duplicates
openhcl/underhill_core/src/worker.rs	Implements write_provisioning_marker() to write diagnostic information when VMGS is provisioned
openhcl/underhill_core/Cargo.toml	Adds tpm_protocol and vmgs_ext dependencies
opentmk/Cargo.toml	Adds tpm_protocol dependency
Cargo.toml	Registers vmgs_ext workspace member
Cargo.lock	Updates with vmgs_ext and new dependencies