[CODE HEALTH] Move func_grpc_main classes into anonymous namespace (#4129)

Wraps the 3 file-scope class and struct declarations in
functional/otlp/func_grpc_main.cc within an anonymous namespace to
give them internal linkage and clear the misc-use-internal-linkage
warnings clang-tidy reports on this file.

The wrap covers TestResult (line 63), TestLogHandler (line 128), and
test_case (line 316). It deliberately ends BEFORE the static int
test_*() forward declarations at line 322+.

This boundary follows the same pattern as #4128 (func_http_main):
the test_*() declarations are matched by definitions in the lower
half of the file (after main()). Wrapping the declarations alone
would create (anonymous namespace)::test_* symbols that fail to
link against the file-scope static test_*() definitions. Local
verification: build of func_otlp_grpc target with
WITH_OTLP_HTTP=ON + WITH_OTLP_GRPC=ON succeeded 122/122 ninja steps;
--help smoke test prints usage as expected.

main() and all test_*() infrastructure (declarations, the
all_tests[] table, list_test_cases, run_test_case, and definitions)
remain at file scope with their existing static linkage.

Ratchet:
* abiv1-preview warning_limit lowered from 349 to 346
* abiv2-preview warning_limit lowered from 353 to 350

Part of #2053

Signed-off-by: thc1006 <84045975+thc1006@users.noreply.github.com>

Author: thc1006

.github/workflows/clang-tidy.yaml

@@ -17,9 +17,9 @@ jobs:
       matrix:
         include:
           - cmake_options: all-options-abiv1-preview
-            warning_limit: 349
+            warning_limit: 346
           - cmake_options: all-options-abiv2-preview
-            warning_limit: 353
+            warning_limit: 350
     env:
       CC: /usr/bin/clang-22
       CXX: /usr/bin/clang++-22

CHANGELOG.md

@@ -51,6 +51,9 @@ Increment the:
 * [CODE HEALTH] Move func_http_main classes into anonymous namespace
   [#4128](https://github.com/open-telemetry/opentelemetry-cpp/pull/4128)
 
+* [CODE HEALTH] Move func_grpc_main classes into anonymous namespace
+  [#4129](https://github.com/open-telemetry/opentelemetry-cpp/pull/4129)
+
 ## [1.27.0] 2026-05-13
 
 * [RELEASE] Bump main branch to 1.27.0-dev

functional/otlp/func_grpc_main.cc

@@ -56,6 +56,9 @@ static std::string opt_cert_dir;
 static std::string opt_test_name;
 static TestMode opt_mode = TestMode::kNone;
 
+namespace
+{
+
 /*
   Log parsing
 */
@@ -319,6 +322,8 @@ struct test_case
   test_func_t m_func;
 };
 
+}  // namespace
+
 static int test_basic();
 
 static int test_cert_not_found();