Feature/secure random value generation

[BavyaMittal]

Title: Replaced os.urandom with secrets.token_bytes for secure random value generation.

Summary:
This pull request replaces all occurrences of os.urandom with the secrets package to improve the security and readability of random value generation. The secrets package is specifically designed for cryptographic purposes, making it a more suitable choice for these use cases. All required imports for secrets have been added.

Testing:
Ran pytest tests/ to verify functionality. All existing tests pass except one, which fails due to exceeding the Hypothesis deadline. The failure is unrelated to these changes and can be addressed by increasing the Hypothesis deadline from 200ms to 500ms.

Error Details for Test:

hypothesis.errors.DeadlineExceeded: Test took 253.70ms, which exceeds the deadline of 200.00ms
Falsifying example: test_key_derivation_from_password(
    password='00000000',
  salt=b'\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00)

[Veinar]

Hi @BavyaMittal 👋,

Everything looks great, the test using hypothesis is not yet fully validated and may cause problems, so don't bother ☺️.

I would just ask you to remove venv because it got into the commit, either by accident or by my bad instructions in CONTRIBUTING.md. And thank you, for your work, many thanks!

[BavyaMittal]

Hi @Veinar Sure! I have deleted the required files.

[Veinar]

Now it is perfect 🙌

[Veinar]

Merged, and it will be used within next release!
Thank you @BavyaMittal once more 🙌

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Files with missing lines	Coverage Δ
envcloak/encryptor.py	96.11% <100.00%> (+0.03%)	⬆️
envcloak/generator.py	95.23% <100.00%> (+0.23%)	⬆️