Expose attachment content decryption via WASM SDK bindings (#220)

## 🎟️ Tracking
Related to https://bitwarden.atlassian.net/browse/PM-12423
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## 📔 Objective
Expose attachment content decryption method to enable TS client-side
file decryption without requiring a separate decrypted key.
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you're fixing or new feature you're adding. -->

## ⏰ Reminders before review

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- Written new unit and / or integration tests where applicable
- Protected functional changes with optionality (feature flags)
- Used internationalization (i18n) for all UI strings
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- Updated any necessary documentation (Confluence, contributing docs) or
informed the documentation
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Author: gbubemismith

crates/bitwarden-wasm-internal/src/vault/attachments.rs

@@ -0,0 +1,24 @@
+use bitwarden_vault::{Attachment, Cipher, DecryptError};
+use wasm_bindgen::prelude::wasm_bindgen;
+
+#[wasm_bindgen]
+pub struct ClientAttachments(bitwarden_vault::ClientAttachments);
+
+impl ClientAttachments {
+    pub fn new(client: bitwarden_vault::ClientAttachments) -> Self {
+        Self(client)
+    }
+}
+
+#[wasm_bindgen]
+impl ClientAttachments {
+    /// Decrypts an attachment's encrypted content
+    pub fn decrypt_buffer(
+        &self,
+        cipher: Cipher,
+        attachment: Attachment,
+        encrypted_buffer: &[u8],
+    ) -> Result<Vec<u8>, DecryptError> {
+        self.0.decrypt_buffer(cipher, attachment, encrypted_buffer)
+    }
+}

crates/bitwarden-wasm-internal/src/vault/mod.rs

@@ -1,7 +1,9 @@
+pub mod attachments;
 pub mod ciphers;
 pub mod folders;
 pub mod totp;
 
+use attachments::ClientAttachments;
 use ciphers::ClientCiphers;
 use totp::ClientTotp;
 use wasm_bindgen::prelude::*;
@@ -19,6 +21,10 @@ impl VaultClient {
 
 #[wasm_bindgen]
 impl VaultClient {
+    pub fn attachments(&self) -> ClientAttachments {
+        ClientAttachments::new(self.0.attachments())
+    }
+
     pub fn ciphers(&self) -> ClientCiphers {
         ClientCiphers::new(self.0.ciphers())
     }