impl(rest): use SSL_get_all_group_names() with BoringSSL

[colinmoy]

Simplifies how AvailableCryptoGroups() queries supported TLS key-exchange groups when built with BoringSSL:

• Uses BoringSSL's SSL_get_all_group_names() function to get the list of supported TLS groups directly, replacing the previous workaround that combined EC_get_builtin_curves() with trial-and-error calls to SSL_CTX_set1_curves_list().
• Checks #if defined(SSL_GROUP_SECP256R1) to verify that the installed BoringSSL version is new enough to have SSL_get_all_group_names() (both were added in the same BoringSSL commit).
• For older BoringSSL versions that don't have SSL_get_all_group_names(), returns an empty list so BoringSSL keeps its default TLS groups (those older versions predate X25519MLKEM768 support anyway).

[gemini-code-assist]

Code Review

This pull request refactors the AvailableCryptoGroups function in ssl_ec_curves.cc to use SSL_get_all_group_names for newer BoringSSL versions, replacing the previous approach of probing candidate curves with a temporary SSL_CTX. It also simplifies preprocessor checks and removes the unused <array> header. The feedback suggests caching the retrieved crypto groups in static variables to avoid repeated heap allocations and library queries on every function call.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.39%. Comparing base (7af76ee) to head (e987590).

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16566      +/-   ##
==========================================
+ Coverage   92.37%   92.39%   +0.01%     
==========================================
  Files        2265     2265              
  Lines      219470   219457      -13     
==========================================
+ Hits       202745   202770      +25     
+ Misses      16725    16687      -38     

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