Fix: JSON import UTF-8 BOM handling issue

[Shyam-Raghuwanshi]

Fix JSON import UTF-8 BOM handling issue

• Add strip_utf8_bom() function to remove UTF-8 BOM (EF BB BF) from file content
• Apply BOM stripping to JsonLines and JsonArray import formats
• Add comprehensive tests for UTF-8 BOM handling across all import formats
• Ensure backward compatibility with files without BOM
• Fix 'Not valid JSON: expected value at line 1 column 1' error for BOM files

fix #138

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[nipunn1313]

Hi.
We ended up fixing clientside with

b671cd8

We thought about doing something serverside, but ended up deciding that BOM was not supported by the server - and we preferred solutions that errors if a BOM is sent up.

Currently, it still says
'Not valid JSON: expected value at line 1 column 1'

If you could modify the PR to give a more specific error in this case, we'd take that instead, but we'd like to keep BOM as unsupported.

[nipunn1313]

Sorry - I didn't follow up on #138 promptly

[nipunn1313]

overall looks good - thanks
One comment.

[nipunn1313]

cool looks good. I'll merge it in later.

[nipunn1313]

merged in 42a8752

@Shyam-Raghuwanshi - I made some small changes to your PR to simplify. Take a look - trying to really make the diff more minimal from the previous behavior.