Replace MD5 with SHA-256 in `hasher` function for improved security

[kexinoh]

Issue Description:

The hasher function in tf_quant_finance/experimental/pricing_platform/framework/utils.py currently uses the MD5 hash algorithm, which is considered insecure for cryptographic purposes due to its vulnerability to collision attacks. While the function is described as returning a "non-cryptographic hash," it would be prudent to replace MD5 with a more secure hash function like SHA-256 to future-proof the code and align with best practices.

Current Code:

def hasher(obj):
  """Returns non-cryptographic hash of a JSON-serializable object."""
  h = hashlib.md5(json.dumps(obj).encode())
  return h.hexdigest()

Proposed Change:
Replace hashlib.md5 with hashlib.sha256.

Proposed Code:

def hasher(obj):
  """Returns non-cryptographic hash of a JSON-serializable object."""
  h = hashlib.sha256(json.dumps(obj).encode())
  return h.hexdigest()

Location:
utils.py#L20

Justification:

• SHA-256 is more secure and widely accepted for hashing purposes.
• This change would improve the robustness of the code without significantly impacting performance.

Additional Context:

• MD5 is still used in non-cryptographic contexts, but SHA-256 is a better choice for future-proofing and maintaining a higher security standard.

Conclusion:
Please consider updating the hasher function to use SHA-256 instead of MD5.

Thank you for your attention to this matter.