fix correct file format parsing

[viveksahu26]

closes: #353

This PR addresses the following:

Previously, it was assumed that if decoding failed, the file format must be incorrect. However, decoding failures can occur for several reasons:

• Invalid format (expected case).
• Structural or syntax errors in the content (unexpected case).
• Empty or malformed content (e.g., newline-only content).

For example, a user-provided SBOM in JSON format with a content error (newline characters) was incorrectly assumed to be a non-JSON file because decoding failed. This was a misconception.

To address this, the format is now validated first:

• If the content starts with "{" or "[", it is identified as JSON.
• If the content starts with ":" or "-", it is identified as YAML.

Once the format is determined, the corresponding switch-case for JSON or YAML is executed. Any subsequent decoding failures are correctly identified as content issues rather than format misidentification. This ensures more robust and accurate handling of SBOM files.