[ntuple] Add support for `(unsigned) long long` fields

[enirolf]

This PR adds support for (unsigned) long long fields, and in addition points (U)Long64_t-type fields here, instead of to std::(u)int64_t.

Still left TODO is properly check the width of this type, as well as long across different platforms

[bellenot]

FYI, on Windows, long is 32 bit on both x86 AND x64

[github-actions[bot]]

Test Results

     8 files       8 suites   2d 4h 18m 57s :stopwatch:  2 577 tests  2 577 :white_check_mark: 0 :zzz: 0 :x: 20 403 runs  20 403 :white_check_mark: 0 :zzz: 0 :x:

Results for commit 940781c6.

:recycle: This comment has been updated with latest results.

[jblomer]

We may not need the template specialization in RColumnElement and RFieldVisitor. I think it should be enough to make the special treatment in RField. Let's discuss tomorrow.

[hahnjo]

FYI, on Windows, long is 32 bit on both x86 AND x64

Yes; this PR is about long long which is guaranteed to be at least 64 bits by C++11.

[enirolf]

It's unclear to me why clang-format fails here. The supposed style violations seem to be in accordance to our .clang-format file and running clang-format locally no violations are reported..

[jblomer]

I guess this has been replaced by #16039