Support returning types with non-static lifetime - Part 2

[fzyzcjy]

Changes

Please list issues fixed by this PR here, using format "Fixes #the-issue-number".

Checklist

• An issue to be fixed by this PR is listed above.
• New tests are added to ensure new features are working. Please refer to this page to see how to add a test.
• ./frb_internal precommit --mode slow (or fast) is run (it internal runs code generator, does auto formatting, etc).
• If this PR adds/changes features, documentations (in the ./website folder) are updated.
• CI is passing. Please refer to this page to see how to solve a failed CI.

Remark for PR creator

• ./frb_internal --help shows utilities for development.
• If fzyzcjy does not reply for a few days, maybe he just did not see it, so please ping him.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.12%. Comparing base (256ed44) to head (32c4796).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2093      +/-   ##
==========================================
+ Coverage   94.30%   99.12%   +4.81%     
==========================================
  Files         479      484       +5     
  Lines       17878    19546    +1668     
==========================================
+ Hits        16860    19374    +2514     
+ Misses       1018      172     -846     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.