mid-types: the wire format as a no_std leaf; mid-verify no_std over it

[Ttimmahlax]

What

• mid-types (new): the mID wire-format types (MidJwtPayload, ClaimValue, AttestedBy, EmbeddedGenesisRoster, EmbeddedRosterChainEntry, VerificationMethod, EmbeddedVerificationMethod, the request types) and canonical::{genesis_canonical_bytes, chain_entry_canonical_bytes}, moved verbatim out of mid-issuer. no_std + alloc; std (default) only forwards to serde and serde_json. The unit tests moved with them.
• mid-issuer depends on mid-types and re-exports everything from the same module paths (mid_issuer::types::*, mid_issuer::canonical::*, and the pub use in the root), so no consumer changes.
• mid-verify depends on mid-types instead of mid-issuer, is #![no_std] with alloc, and gains a std default feature that forwards to its dependencies. thiserror moves to 2.x for the no_std derive.

Why

A device that signs its own genesis roster and self-issued token — the Janus ESP32 family (rusty_esp_mid) — was carrying a copy of these types. It now imports them from mid-types; its oracle tests, which compare its canonical bytes with mid-issuer's and verify its tokens with mid-verify, pass unchanged (28 unit + 7 oracle tests, including a byte-identical genesis-roster canonical form). A verifier that fits a chip is the second half of the same seam.

API changes (please read)

• VerifyError::Base64Decode { segment, source } → { segment, cause }. base64 implements the error trait only with std, so the field cannot be an implicit source on the no_std arm; under std it is still marked #[source].
• VerifyError::PayloadJson keeps From<serde_json::Error> (hand-written) and its #[source] under std.
• Everything else is path-compatible.

Gates run here

gate	result
cargo test -p mid-types -p mid-verify	10 + 26 green
cargo check -p mid-types -p mid-verify --no-default-features --target riscv32imac-unknown-none-elf	clean
cargo check --workspace	clean
cargo clippy -p mid-types -p mid-verify --all-targets -- -D warnings	clean; kms-client already fails clippy on main (a generic-array deprecation in signer.rs:94), untouched here
downstream: rusty_esp_mid-core on this branch	28 unit + 7 oracle tests green, riscv32imac with and without alloc

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