refactor(mcuboot): contain TLV info magics in the type system

[JPHutchins]

Summary

• ImageMagic, ImageTLVInfoMagic, and ImageTLVProtInfoMagic Literal type aliases tie each magic constant to its type (Literal[...] cannot reference a Final name per PEP 586, so the constants are typed Final[<alias>] to keep the value and type checked against each other).
• ImageTLVInfo is now generic over its magic, so protected and unprotected TLV info regions are distinct static types. The expected magic argument to loads/load_from binds the type parameter and supplies the runtime check, replacing the protected: bool flag. The loaders use a method-scoped TypeVar (MagicT) because class-scoped TypeVars only bind via self/cls — verified against both mypy and pyright.
• ImageTLVInfo.load_tlvs_from(file) reads and parses the TLV entries that follow the header, removing the tlv_tot - IMAGE_TLV_INFO_STRUCT.size wire-format arithmetic from ImageInfo.load_file.
• ImageHeader bad-magic validation moves from __post_init__ (made unreachable by pydantic Literal validation) into loads, preserving MCUBootImageError on the load path.
• Tests: assert_type checks pin the static types at call sites, and new error-path tests bring smpclient/mcuboot.py to 100% line and branch coverage.

Breaking changes

• ImageTLVInfo.loads/load_from take a required magic argument instead of protected: bool = False.
• ImageTLVInfo.REGION_SIZE is removed — use IMAGE_TLV_INFO_STRUCT.size.
• ImageInfo.protected_tlvs defaults to None instead of [], pairing with protected_tlv_info.

Test plan

• task format, task lint, task typecheck (mypy), full task test — 296 passed
• pyright clean on mcuboot.py and test_mcuboot_tools.py (loaders infer ImageTLVInfo[Literal[0x6907]]/[Literal[0x6908]], no Unknown)
• 100% line and branch coverage on smpclient/mcuboot.py

🤖 Generated with Claude Code

[JPHutchins]

FYI @ChapterSevenSeeds - stronger typing for mcuboot types, claude pass for "100% coverage".

[Copilot]

Pull request overview

This PR refactors the MCUBoot image parsing utilities to encode MCUBoot “magic” constants (image header magic and TLV info/protected TLV info magics) directly in the type system using Literal aliases and a generic ImageTLVInfo[T]. It simplifies TLV parsing by moving “read following TLVs” logic onto the TLV-info header type and strengthens error-path behavior with additional tests.

Changes:

• Introduces Literal-backed magic types (ImageMagic, ImageTLVInfoMagic, ImageTLVProtInfoMagic) and makes ImageTLVInfo generic over its magic.
• Updates TLV-info loading APIs to require an explicit expected magic (replacing the previous protected: bool flag) and adds ImageTLVInfo.load_tlvs_from(...) to encapsulate TLV-region parsing.
• Adjusts ImageInfo protected TLV fields (protected_tlvs now None by default) and expands tests with type-binding assertions and additional error-path coverage.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/smpclient/mcuboot.py	Refactors magic constants into Literal types, generifies TLV-info headers, moves magic validation to load paths, and encapsulates TLV region parsing.
tests/test_mcuboot_tools.py	Adds assert_type checks for the new generic types and expands regression/error-path test coverage for the refactor.

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