feat: migrate to FIPS-validated cryptographic algorithms (#3423)

# What does this PR do?
Migrates MD5 and SHA-1 hash algorithms to SHA-256.

In particular, replaces:   
   - MD5 in chunk ID generation.
   - MD5 in file verification.
   - SHA-1 in model identifier digests.

And updates all related test expectations.

Original discussion:
https://github.com/llamastack/llama-stack/discussions/3413

<!-- If resolving an issue, uncomment and update the line below -->
Closes #3424.

## Test Plan
Unit tests from scripts/unit-tests.sh were updated to match the new hash
output, and ran to verify the tests pass.

Signed-off-by: Doug Edgar <dedgar@redhat.com>

llama_stack/providers/utils/vector_io/vector_utils.py

@@ -12,14 +12,12 @@ import uuid
 def generate_chunk_id(document_id: str, chunk_text: str, chunk_window: str | None = None) -> str:
     """
     Generate a unique chunk ID using a hash of the document ID and chunk text.
-
-    Note: MD5 is used only to calculate an identifier, not for security purposes.
-    Adding usedforsecurity=False for compatibility with FIPS environments.
+    Then use the first 32 characters of the hash to create a UUID.
     """
     hash_input = f"{document_id}:{chunk_text}".encode()
     if chunk_window:
         hash_input += f":{chunk_window}".encode()
-    return str(uuid.UUID(hashlib.md5(hash_input, usedforsecurity=False).hexdigest()))
+    return str(uuid.UUID(hashlib.sha256(hash_input).hexdigest()[:32]))
 
 
 def proper_case(s: str) -> str: