Add Field Descriptor Deserialization Logic

[Krmjn09]

This PR adds the logic to read field descriptors from the RNTuple header. It includes:

1. Reading envelope and metadata like name, description, and writer
2. Parsing the list of field records (name, type, flags, etc.)
3. Handling optional values like array size or checksum based on flags

However, there's an issue: the code throws an offset out of bounds error while reading. I've tried multiple approaches but haven’t been able to debug the reason of error yet.

[silverweed]

Why have you created a second PR that overlaps with #334? Isn't this introducing the same changes?

[Krmjn09]

Why have you created a second PR that overlaps with #334? Isn't this introducing the same changes?

I felt the previous pr failed , became really messy and confusing so created a new pr which only have right now field descriptor logic then in the future pr I will add rest of the logic taking the #334 pr as help

[silverweed]

In general it's not great to "restart fresh" with PRs because you lose track of all comments and history of changes. In this case it may work because the amount of code changes is small, but still there are 4 or 5 comments of mine on the old PR which still need to be addressed.
What you should do if you think the history of changes has become too messy is squashing together some (or all) the commits using git rebase -i dev and then force-push over your development branch (git push -f <your_remote> feature/deserializing-header)

[Krmjn09]

In general it's not great to "restart fresh" with PRs because you lose track of all comments and history of changes. In this case it may work because the amount of code changes is small, but still there are 4 or 5 comments of mine on the old PR which still need to be addressed. What you should do if you think the history of changes has become too messy is squashing together some (or all) the commits using git rebase -i dev and then force-push over your development branch (git push -f <your_remote> feature/deserializing-header)

Okay, Thankyou so much for telling me this .I will keep this in mind in the future

[silverweed]

A couple of minor things before merging

[Krmjn09]

@silverweed this >>> is givinng error , I think Javascript throws error when we use >>> on BigInt Numbers

[silverweed]

Thanks!