feat(webauthn): perform largeBlob.read via authenticatorLargeBlobs

Adds the read-path helper for the WebAuthn L3 largeBlob extension. After
get_assertion returns a largeBlobKey, the platform paginates
authenticatorLargeBlobs(get), AES-256-GCM-authenticates each entry under
the per-credential key, and RFC 1951 raw-deflate decompresses the
plaintext into unsigned_extensions_output.large_blob.blob.

Read failures surface as blob absent, per WebAuthn L3 sec 10.1.5. The
chunk size honours maxFragmentLength = maxMsgSize - 64 from GetInfo.
origSize is capped at 1 MiB to bound platform allocation. Per-entry
structural problems are skipped, not propagated, since the on-device
array is shared across credentials.

Author: AlfioEmanueleFresta

Cargo.lock

@@ -70,6 +70,8 @@ p256 = { version = "0.13.2", features = ["ecdh", "arithmetic", "serde"] }
 heapless = "0.7"
 cosey = "0.3.2"
 aes = "0.8.2"
+aes-gcm = "0.10"
+flate2 = "1.0"
 hmac = "0.12.1"
 cbc = { version = "0.1", features = ["alloc"] }
 hkdf = "0.12"