THRIFT-5785: fix boost include

[CJCombrink]

Remove another boost header include from the public API

• It is only used in THeaderTransport.cpp so move it there without complicating it
• It throws a TTransportException so it should not be used in other code
• People that depends on this can use boost::numeric_cast or std::in_range (C++20) instead
• The usage in the unit test was not needed since std::string::size() returns an unsigned long on 64-bit compilers

• Did you create an Apache Jira ticket? THRIFT-5785
• If a ticket exists: Does your pull request title follow the pattern "THRIFT-NNNN: describe my issue"?
• Did you squash your changes to a single commit? (not required, but preferred)
• Did you do your best to avoid breaking changes? If one was needed, did you label the Jira ticket with "Breaking-Change"?
• If your change does not involve any code, include [skip ci] anywhere in the commit message to free up build resources.

The following tickets are releated

• THRIFT-5660
• THRIFT-5785

[CJCombrink]

PS: just rewriting the offending function without using boost was more complex than I have anticipated (see the linked tickets)
On closer inspection I realised that just moving the function internal removes the problem thus no complex code changes needed

[emmenlau]

Looks good to me. I did not check test results. If tests are green, please merge!

[hdu-sdlzx]

lgtm
I can build my project with installed thrift and without boost now.