fix: building with -D_LIBCPP_REMOVE_TRANSITIVE_INCLUDES

[tachalorah]

Fixes these missing header errors when building with clang++ -D_LIBCPP_REMOVE_TRANSITIVE_INCLUDES:

src/common/file-utils.cpp:346:24: error: use of undeclared identifier
      'getenv'
  346 |     const char *home = getenv("HOME");
      |                        ^~~~~~
1 error generated.
<...>
src/lib/crypto/mem.h:78:32: error: no member named 'calloc' in
      namespace 'std'; did you mean simply 'calloc'?
   78 |         ptr = static_cast<T *>(std::calloc(n, sizeof(T)));
      |                                ^~~~~~~~~~~
      |                                calloc
/usr/include/sched.h:83:8: note: 'calloc' declared here
   83 | void *(calloc)(size_t, size_t);
      |        ^
<...>
src/lib/crypto/mem.h:95:14: error: no type named 'free' in namespace
      'std'
   95 |         std::free(p);
      |         ~~~~~^
2 errors generated.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.36%. Comparing base (8cb2718) to head (72d3feb).
⚠️ Report is 43 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2453      +/-   ##
==========================================
- Coverage   85.36%   85.36%   -0.01%     
==========================================
  Files         126      126              
  Lines       22860    22860              
==========================================
- Hits        19515    19514       -1     
- Misses       3345     3346       +1     

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