Add SecretKey for typed symmetric encryption

[Sébastien Duquette (sduquette-devolutions)]

Add a wrapped SecretKey type analogous to PrivateKey/PublicKey.
Ciphertext::encrypt_with_secret_key and Ciphertext::decrypt_with_secret_key
take the key as a SecretKey instead of raw bytes.

Methods encrypt_with_raw_key and decrypt_with_raw_key were defined,
encrypt/decrypt call these methods.

[Copilot]

Pull request overview

This PR introduces a typed SecretKey wrapper for symmetric encryption (analogous to existing wrapped key types) and threads it through the Rust core API and multiple language wrappers (WASM/JS, UniFFI, Python, C FFI, and C#), along with tests and demo updates.

Changes:

• Added Rust key::SecretKey (KeySubtype::Secret) with generation, serialization, and parsing support.
• Added typed symmetric encryption/decryption APIs that accept &SecretKey, plus wrapper exports across WASM/UniFFI/Python/FFI/C#.
• Added new/updated tests (Rust + conformity + Python + C# + WASM) and an Angular demo page for SecretKey encryption.

Reviewed changes

Copilot reviewed 31 out of 32 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
wrappers/wasm/wasm_build.ps1	New PowerShell build helper for wasm-pack targets and renames the web package in dist.
wrappers/wasm/tests/tests/symmetric.ts	Adds JS/WASM tests for encrypt/decrypt using SecretKey (with and without AAD).
wrappers/wasm/demo/src/app/service/encryption.inner.service.ts	Re-exports SecretKey and adds helper functions for SecretKey operations in the demo service layer.
wrappers/wasm/demo/src/app/secret-key-encryption/secret-key-encryption.component.ts	New Angular component demonstrating SecretKey generation + encrypt/decrypt flows.
wrappers/wasm/demo/src/app/secret-key-encryption/secret-key-encryption.component.html	Template for the new demo page UI.
wrappers/wasm/demo/src/app/app.routes.ts	Adds route for the SecretKey encryption demo page.
wrappers/wasm/demo/src/app/app.component.html	Adds navigation link to the new SecretKey encryption demo page.
wrappers/wasm/demo/package.json	Switches demo to consume the locally built ../dist/web package.
wrappers/wasm/demo/package-lock.json	Updates lockfile for the local ../dist/web dependency.
wrappers/python/tests/symmetric.py	Adds Python tests for SecretKey encrypt/decrypt (with and without AAD).
wrappers/csharp/tests/unit-tests/TestManaged.cs	Adds C# unit tests for SecretKey generation, encrypt/decrypt, AAD handling, and round-trip serialization.
wrappers/csharp/tests/unit-tests/Conformity.cs	Adds a conformity test vector for decrypting V2 ciphertext with a wrapped SecretKey.
wrappers/csharp/src/SecretKey.cs	Introduces a C# SecretKey wrapper type for serialized secret-key blobs.
wrappers/csharp/src/Native.Core.cs	Adds P/Invoke bindings for GenerateSecretKey and GenerateSecretKeySize.
wrappers/csharp/src/Managed.cs	Adds SecretKey generation and encrypt/decrypt overloads taking SecretKey.
uniffi/devolutions-crypto-uniffi/src/key.rs	Exposes SecretKey generation via UniFFI (serialized bytes).
uniffi/devolutions-crypto-uniffi/src/ciphertext.rs	Exposes encrypt/decrypt helpers that accept serialized SecretKey bytes (and AAD variants).
tests/conformity.rs	Adds Rust-level conformity test vector for decrypting with a wrapped SecretKey.
src/wasm.rs	Exposes SecretKey as a wasm-bindgen class plus typed encrypt/decrypt bindings.
src/secret_sharing/mod.rs	Doc text cleanup (“split” vs “splitted”).
src/lib.rs	Updates crate docs to reflect SecretKey support and adjusts exports.
src/key/secret_key_v1.rs	Implements SecretKey V1 payload (32 random bytes, zeroized).
src/key/mod.rs	Adds SecretKey wrapper type, generation, serialization/deserialization, and tests.
src/enums.rs	Adds KeySubtype::Secret = 4.
src/ciphertext/mod.rs	Adds *_with_raw_key helpers, plus typed SecretKey encrypt/decrypt wrappers and tests.
README_RUST.md	Removes/updates badges in Rust README.
python/src/lib.rs	Adds Python bindings for generate_secret_key, encrypt_with_secret_key, decrypt_with_secret_key.
python/devolutions_crypto.pyi	Adds Python type stubs/docs for new SecretKey functions.
ffi/src/lib.rs	Adds C ABI GenerateSecretKey + size function and a unit test.
ffi/devolutions-crypto.h	Adds C header declarations for SecretKey generation functions.
_plans/secret-key.md	Adds implementation plan document for Rust core SecretKey.
_plans/secret-key-wrappers.md	Adds implementation plan document for exposing SecretKey in wrappers.

Files not reviewed (1)

• wrappers/wasm/demo/package-lock.json: Language not supported

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[mmorrissette-devolutions]

LGTM