fix: declare FIPS service-indicator funcs in curve25519.c

[dougch]

Issues:

No GitHub issue. Root cause surfaced by the clang-tidy run on #3477 (RFC 8032 Duvet annotations), which added comment lines adjacent to these calls and re-triggered a pre-existing implicit-function-declaration warning. This PR fixes the underlying cause independently of that annotation work.

Description of changes:

crypto/fipsmodule/curve25519/curve25519.c calls FIPS_service_indicator_lock_state() / FIPS_service_indicator_unlock_state() but does not include the header that declares them, crypto/fipsmodule/service_indicator/internal.h. Nothing in its existing include chain reaches that header (the public <openssl/service_indicator.h> does not declare the lock/unlock functions), so the calls rely on an implicit function declaration.

This change adds #include "../service_indicator/internal.h", matching the 12 other fipsmodule translation units that use these functions (e.g. hmac.c, ec_key.c, ecdh.c, e_aesccm.c).

Call-outs:

• No functional change today: in FIPS builds the module links as a unit and the real symbol resolves; the assumed int f() prototype vs. actual void f(void) is harmless for a no-arg call.
• The fix matters as latent correctness: implicit declarations are a hard error under C23 / newer clang, and in non-FIPS builds the missing include bypasses the intended OPENSSL_INLINE no-op definition.

Testing:

No new tests. Covered by existing curve25519/Ed25519 suites; the change only makes an already-used declaration visible. Verified the include path matches sibling fipsmodule files.

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.

[github-actions]

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Please review before merging.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.40%. Comparing base (e4117b4) to head (6520bfe).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3514      +/-   ##
==========================================
+ Coverage   78.36%   78.40%   +0.03%     
==========================================
  Files         700      700              
  Lines      125684   125684              
  Branches    17377    17377              
==========================================
+ Hits        98490    98539      +49     
+ Misses      26322    26272      -50     
- Partials      872      873       +1     

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