Fix Julia, Lua, and OCaml test failures

- Julia: Rename test() to run_test() to avoid name collision
- Julia: Use lambda syntax instead of do-block for cleaner execution
- Lua: Fix signature format test - verify structure instead of counting colons
- OCaml: Use apt-get instead of failing setup-ocaml@v2 action

tests/unit/test_lua.lua

@@ -162,15 +162,14 @@ test("Signature format is timestamp:METHOD:path:body", function()
     local timestamp = "1704067200"
     local method = "POST"
     local endpoint = "/execute"
-    local body = '{"language":"python","code":"print(1)"}'
+    local body = '{"language":"python"}'
 
     local message = timestamp .. ":" .. method .. ":" .. endpoint .. ":" .. body
 
-    assert_contains(message, ":")
-    local count = 0
-    for _ in message:gmatch(":") do count = count + 1 end
-    assert_equal(count, 3)
+    -- Verify format by checking structure, not counting colons (body may contain colons)
     assert_true(message:sub(1, #timestamp) == timestamp)
+    assert_contains(message, ":POST:")
+    assert_contains(message, ":/execute:")
 end)
 
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