Add support for PKCS7_set/get_detached

[samuel40791765]

Description of changes:

We’re still missing two PKCS7 symbols: https://github.com/aws/aws-lc/actions/runs/12898691659/job/35966230534#step:4:4012 This also applies to past releases.

• PKCS7_get_detached is basically an alias to PKCS7_is_detached, so I've done that accordingly.
• PKCS7_set_detached is used to "detach" data contents from the internal PKCS7 structure. The OpenSSL code uses a detached field in the PKCS7 structure that’s missing in AWS-LC. This field isn't necessarily needed though, we can just detect the functionality accordingly.

Call-outs:

N/A

Testing:

New tests

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license and the ISC license.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 78.94737% with 4 lines in your changes missing coverage. Please review.

Project coverage is 78.94%. Comparing base (29be983) to head (a712d2c).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
crypto/pkcs7/pkcs7.c	75.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2134      +/-   ##
==========================================
- Coverage   78.95%   78.94%   -0.01%     
==========================================
  Files         610      610              
  Lines      105293   105312      +19     
  Branches    14911    14924      +13     
==========================================
+ Hits        83129    83141      +12     
- Misses      21511    21517       +6     
- Partials      653      654       +1     

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[justsmth]

The semantic of the detach parameter is unexpected. The call always "fails" (returns 0) when detach = 0.

Could we detect detach == 0 and return 0 at the top? (The difference would be that calls to OPENSSL_PUT_ERROR in certain situations would not be made.)

if (detach != 1) {
    return 0;
}

If the calls to OPENSSL_PUT_ERROR are important, we should have test coverage to confirm they are made.

[samuel40791765]

The detach parameter is expected to be consumed as a boolean. Ruby has a good example of the usage here: https://github.com/ruby/ruby/blob/dd863714bf377b044645ea12b4db48920d49694e/ext/openssl/ossl_pkcs7.c#L497-L500

I completely agree with the weird semantic of the detach parameter, especially with 0. OpenSSL's implementation allows for other numbers to be used, but seeing that it doesn't align with how the API was meant to be used, I decided to restrict the values to only 0 and 1.
Since the parameter value was meant to take a boolean integer, I do think 0 should be allowed as a value though. I'll add coverage for the unsupported operations.