MDEV-35646: Limit pseudo_thread_id to UINT32_MAX

[ParadoxV5]

• The Jira issue number for this PR is: MDEV-35646

What problem is the patch trying to solve?

Although the my_thread_id type is 64 bits, binlog format specs limits it to 32 bits in practice. (See also: MDEV-35706)

The writable SQL variable pseudo_thread_id didn’t realize this though and had a range of ULONGLONG_MAX (at least UINT64_MAX in C/C++).
It consequentially accepted larger values silently, but only the lower 32 bits of whom gets binlogged; this could lead to inconsistency.

Release Notes

The internal variable pseudo_thread_id is now limited to 32 unsigned bits (max. 4294967295) to match the range of thread_id.

How can this PR be tested?

The MTR tests sys_vars.sysvars_server_notembedded and sys_vars.sysvars_server_embedded covers the SQL variable pseudo_thread_id itself.
I got tangled by our #include struture, so I split my plan to fix the aformentioned inconsistency once and for all to MDEV-35706. Solving this would also remedy any truncation that originates not from the user but from our own 🍝.
I skimmed through git grep pseudo_thread_id and found not much though, so capping the SQL variable should be sufficient (unless the system vars constructor is broken).

Basing the PR against the correct MariaDB version

• This is a new feature or a refactoring, and the PR is based against the main branch.
• This is a bug fix, and the PR is based against the earliest maintained branch in which the bug can be reproduced.

PR quality check

• I checked the CODING_STANDARDS.md file and my PR conforms to this where appropriate.
• For any trivial modifications to the PR, I am ok with the reviewer making the changes themselves.