vmgs: clean up errors and add tracing to vmgstool

[tjones60]

• Replace any remaining anyhow errors in the VMGS implementation and remove any unnecessarily duplicate errors in VmgsTool.
• Adds a tracing subscriber to VmgsTool and converts (almost) all stderr output to use it.
  • This gets us timestamps and logs from internal crates with the new verbose mode enabled.
• Removes the word "Error" from any VmgsTool logs that may not actually indicate an error.

[github-actions]

⚠️ Unsafe Code Detected

This PR modifies files containing unsafe Rust code. Extra scrutiny is required during review.

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[Copilot]

Pull request overview

This PR improves error handling and observability in the VMGS (VM Guest State) implementation by replacing generic anyhow errors with strongly-typed errors and adding comprehensive tracing support to VmgsTool.

Changes:

• Replaces anyhow::Error with specific typed errors in the VMGS library, including new error variants like NeedsUnlock, DecryptMetadataKey, UnexpectedLength, and InvalidArgument
• Adds tracing subscriber to VmgsTool with configurable verbosity levels and converts all eprintln! calls to appropriate tracing levels (info, warn, error)
• Renames methods for clarity: is_encrypted() → encrypted(), is_encrypted_and_unlocked() → encrypted_and_unlocked()
• Updates FileInfoNotAllocated error variant to include the FileId for better error messages
• Adds Display implementation for FileId to improve log output

Reviewed changes

Copilot reviewed 16 out of 17 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
vm/vmgs/vmgs/src/error.rs	Removes anyhow dependency, adds new typed error variants, updates error messages
vm/vmgs/vmgs/src/vmgs_impl.rs	Replaces anyhow! with typed errors, renames encryption check methods, updates error propagation
vm/vmgs/vmgs/src/encrypt/win.rs	Replaces anyhow with typed BCrypt error variant
vm/vmgs/vmgs/src/encrypt/ossl.rs	Replaces String with &'static str in OpenSSL error messages
vm/vmgs/vmgs/Cargo.toml	Removes anyhow dependency, adds windows-result for BCrypt errors
vm/vmgs/vmgstool/src/main.rs	Adds tracing initialization, converts error handling to use tracing, improves exit code handling
vm/vmgs/vmgstool/src/uefi_nvram.rs	Converts eprintln! to tracing::info!, updates method calls
vm/vmgs/vmgstool/src/test.rs	Converts eprintln! to tracing::info!
vm/vmgs/vmgstool/src/storage_backend.rs	Updates FileInfoNotAllocated pattern match for new signature
vm/vmgs/vmgstool/Cargo.toml	Adds tracing dependencies
vm/vmgs/vmgs_format/src/lib.rs	Adds Display implementation for FileId
vm/vmgs/vmgs_broker/src/broker.rs	Updates FileInfoNotAllocated pattern match
openhcl/underhill_attestation/*	Updates all call sites for renamed methods and error patterns
Cargo.toml & Cargo.lock	Adds windows-result workspace dependency