Add extensible hash primitives: SHA1, SHA256, SHA512

Introduces a `crypto` feature (on by default) that wires the RustCrypto
sha1/sha2 crates into a small `HashAlgo` registry. `register_primitives`
iterates `crypto::ALGOS` and installs one Forth host word per algorithm,
each with the stack effect

    ( c-addr u -- c-addr2 u2 )

reading `u` bytes from `c-addr` and writing the digest into a shared
`HASH_SCRATCH` region in linear memory (carved out between the float
stack and the dictionary).

Adding a new hash is a one-line entry in `ALGOS`. `register_host_primitive`
is now `pub` so downstream crates can extend the VM with their own I/O
host words without forking WAFER — kelvar (a deterministic password
manager on WAFER) is the first consumer.

- 4 unit tests (lib-level sha1/256/512 + registry sanity)
- 5 integration tests (in-VM `SHA1`/`SHA256`/`SHA512` against RFC-3174,
  FIPS-180, and the first-round S/KEY seed used by `hel`)
- All 437 existing lib tests still pass; `wafer-web` still builds for
  `wasm32-unknown-unknown` with the feature enabled

Cargo.lock

@@ -141,6 +141,15 @@ dependencies = [
  "generic-array",
 ]
 
+[[package]]
+name = "block-buffer"
+version = "0.12.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cdd35008169921d80bc60d3d0ab416eecb028c4cd653352907921d95084790be"
+dependencies = [
+ "hybrid-array",
+]
+
 [[package]]
 name = "bumpalo"
 version = "3.20.2"
@@ -255,6 +264,12 @@ dependencies = [
  "windows-sys",
 ]
 
+[[package]]
+name = "const-oid"
+version = "0.10.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a6ef517f0926dd24a1582492c791b6a4818a4d94e789a334894aa15b0d12f55c"
+
 [[package]]
 name = "cpp_demangle"
 version = "0.4.5"
@@ -273,6 +288,15 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "cpufeatures"
+version = "0.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8b2a41393f66f16b0823bb79094d54ac5fbd34ab292ddafb9a0456ac9f87d201"
+dependencies = [
+ "libc",
+]
+
 [[package]]
 name = "cranelift-assembler-x64"
 version = "0.130.1"
@@ -459,6 +483,15 @@ dependencies = [
  "typenum",
 ]
 
+[[package]]
+name = "crypto-common"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "77727bb15fa921304124b128af125e7e3b968275d1b108b379190264f4423710"
+dependencies = [
+ "hybrid-array",
+]
+
 [[package]]
 name = "debugid"
 version = "0.8.0"
@@ -474,8 +507,19 @@ version = "0.10.7"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "9ed9a281f7bc9b7576e61468ba615a66a5c8cfdff42420a70aa82701a3b1e292"
 dependencies = [
- "block-buffer",
- "crypto-common",
+ "block-buffer 0.10.4",
+ "crypto-common 0.1.7",
+]
+
+[[package]]
+name = "digest"
+version = "0.11.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4850db49bf08e663084f7fb5c87d202ef91a3907271aff24a94eb97ff039153c"
+dependencies = [
+ "block-buffer 0.12.0",
+ "const-oid",
+ "crypto-common 0.2.1",
 ]
 
 [[package]]
@@ -773,6 +817,15 @@ dependencies = [
  "windows-sys",
 ]
 
+[[package]]
+name = "hybrid-array"
+version = "0.4.10"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3944cf8cf766b40e2a1a333ee5e9b563f854d5fa49d6a8ca2764e97c6eddb214"
+dependencies = [
+ "typenum",
+]
+
 [[package]]
 name = "id-arena"
 version = "2.3.0"
@@ -1422,6 +1475,17 @@ dependencies = [
  "unsafe-libyaml",
 ]
 
+[[package]]
+name = "sha1"
+version = "0.11.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "aacc4cc499359472b4abe1bf11d0b12e688af9a805fa5e3016f9a386dc2d0214"
+dependencies = [
+ "cfg-if",
+ "cpufeatures 0.3.0",
+ "digest 0.11.2",
+]
+
 [[package]]
 name = "sha2"
 version = "0.10.9"
@@ -1429,8 +1493,19 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "a7507d819769d01a365ab707794a4084392c824f54a7a6a7862f8c3d0892b283"
 dependencies = [
  "cfg-if",
- "cpufeatures",
- "digest",
+ "cpufeatures 0.2.17",
+ "digest 0.10.7",
+]
+
+[[package]]
+name = "sha2"
+version = "0.11.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "446ba717509524cb3f22f17ecc096f10f4822d76ab5c0b9822c5f9c284e825f4"
+dependencies = [
+ "cfg-if",
+ "cpufeatures 0.3.0",
+ "digest 0.11.2",
 ]
 
 [[package]]
@@ -1682,6 +1757,8 @@ dependencies = [
  "anyhow",
  "insta",
  "proptest",
+ "sha1",
+ "sha2 0.11.0",
  "thiserror 2.0.18",
  "wasm-encoder 0.246.2",
  "wasmparser 0.246.2",
@@ -2022,7 +2099,7 @@ dependencies = [
  "semver",
  "serde",
  "serde_derive",
- "sha2",
+ "sha2 0.10.9",
  "smallvec",
  "target-lexicon",
  "wasm-encoder 0.245.1",
@@ -2045,7 +2122,7 @@ dependencies = [
  "rustix",
  "serde",
  "serde_derive",
- "sha2",
+ "sha2 0.10.9",
  "toml",
  "wasmtime-environ",
  "windows-sys",