chore: Enable clang-tidy modernize-use-nodiscard check (#7015)

include/xrpl/protocol/STBitString.h

@@ -29,26 +29,26 @@ public:
     STBitString(SField const& n, value_type const& v);
     STBitString(SerialIter& sit, SField const& name);
 
-    SerializedTypeID
+    [[nodiscard]] SerializedTypeID
     getSType() const override;
 
-    std::string
+    [[nodiscard]] std::string
     getText() const override;
 
-    bool
+    [[nodiscard]] bool
     isEquivalent(STBase const& t) const override;
 
     void
     add(Serializer& s) const override;
 
-    bool
+    [[nodiscard]] bool
     isDefault() const override;
 
     template <typename Tag>
     void
     setValue(base_uint<Bits, Tag> const& v);
 
-    value_type const&
+    [[nodiscard]] value_type const&
     value() const;
 
     operator value_type() const;