1.0: drop every runtime dependency, enforce the licensing claims, add MulanPSL-2.0

[paudley]

Three related changes, released together as 1.0.0.

1. Zero runtime dependencies

cargo tree --edges normal now prints only visual-hashing. The ten-crate
graph, the build script and the C-compiler requirement are gone.

The whole graph existed to serve four lines in emojihash that ask BLAKE3 for
nine bytes of XOF output from a 32-byte public key. For a library whose point
is being a small, auditable primitive you embed next to key material, that was
the main defect.

src/blake3.rs implements the part actually needed: unkeyed, one-shot,
extendable output. The reduction comes from dropping the incremental API,
not from capping the input — upstream carries a chunk state, a 54-deep
chaining-value stack and block bookkeeping because update() may be handed any
prefix, whereas a caller supplying the whole slice collapses all of that into
one recursive descent over the subtree structure. Full input range is kept;
capping at one chunk would have saved ~20 lines and eventually returned a wrong
answer for a 2 KB input.

Correctness is checked three ways rather than assumed:

• the frozen vectors under vectors/ pass byte-for-byte unchanged — the
  proof that matters;
• tests/blake3_equivalence.rs keeps the upstream blake3 crate as a dev-only
  oracle and diffs against it across every block, chunk and subtree boundary
  (~600 comparisons);
• published known-answer vectors are pinned in unit tests, so agreement does
  not rest solely on the oracle.

serde_json goes too, replaced by a strict reader for the generated vector
shape that rejects anything outside it — including the key set, so a malformed
vector fails loudly instead of leaving an assertion silently unexercised.

With nothing left to link, the crate is now no_std + alloc and builds for
thumbv7em-none-eabihf as well as wasm32.

2. The claims are enforced, not asserted

The dependency audit came out clean, but a clean audit is a fact about one
afternoon, not a property of the repository.

scripts/check-licenses.py gates the SPDX expression on every tracked file,
agreement between headers and REUSE.toml, the licence-text digests, and the
no-runtime-dependencies property. It found a real gap on its first run:
REUSE.toml carried no header of its own. deny.toml covers advisories,
sources, duplicate versions and the dev-only licence graph.

It is a first-party script rather than a third-party action on purpose — every
action in this workflow is SHA-pinned, and widening the supply chain to run
what amounts to a grep would be a poor trade.

3. MulanPSL-2.0

The crate is now offered under MIT OR Apache-2.0 OR MulanPSL-2.0. OR is
operative: pick one, comply with that one. Nothing is taken from anyone already
using MIT or Apache-2.0. Blackcat Informatics is the sole author of everything
in this tree, so the grant is unilateral.

LICENSING.md documents rather than merely lists it — §6 makes the Chinese
text controlling where the two versions diverge, §2's patent grant ends on
patent litigation, §3 withholds trademarks explicitly, and §4 carries the
notice-retention obligation. Every claim was read off the shipped text. It also
now carries a 中文说明 summarising the grant in Chinese, since documenting a
Chinese-controlling licence only in English serves the wrong audience.

The canonical host (license.coscl.org.cn) is unreachable, so LICENSE-MULAN
is the official bilingual text from the SPDX license-list-data mirror, pinned
by SHA-256 and re-verified in CI.

vectors/ takes the same grant. Those files are generated by this repository's
own scripts from its own reference implementation, and byte-identical copies
are redistributed by purrdf and gmeow-gts; naming this repository canonical
settles a declaration that differed between the three trees.

Verification

cargo fmt --check                                   OK
cargo clippy --all-targets -- -D warnings           OK
cargo test --locked                                 10 passed
cargo tree --edges normal                           visual-hashing only
cargo build --lib --target wasm32-unknown-unknown   OK
cargo build --lib --target thumbv7em-none-eabihf    OK
cargo deny check                                    advisories/bans/licenses/sources ok
python3 scripts/check-licenses.py                   OK
cargo publish --locked --dry-run                    OK  <- crates.io accepts the SPDX expression

4. 1.0

The API and both renderings are frozen, so this ships as 1.0.0 rather than
0.9.0-then-1.0.0 a week apart. What 1.0 commits to: the 64-emoji alphabet, the
randomart ramp and the public API do not change. A fingerprint already printed
in a log, a CLI banner or someone's notes has to keep meaning what it meant, so
altering either rendering would warrant a new crate rather than a new major
version. The frozen vectors hold that line and CI fails on drift.

Downstream note

0.1.3 → 1.0.0 is semver-incompatible, so neither consumer picks this up
automatically — for a 0.x requirement the minor slot is the breaking one,
so "0.1.3" means >=0.1.3, <0.2.0. After this publishes:

File	Change
purrdf/Cargo.toml:187 (workspace table)	visual-hashing = "1"
gmeow-gts/rust/Cargo.toml:58	visual-hashing = "1"

The public API and every rendering are unchanged.