Merge bitcoin/bitcoin#25707: refactor: Make const references to avoid unnecessarily copying objects and enable two clang-tidy checks

ae7ae36d31 tidy: Enable two clang-tidy checks (Aurèle Oulès)
081b0e53e3 refactor: Make const refs vars where applicable (Aurèle Oulès)

Pull request description:

  I added const references to some variables to avoid unnecessarily copying objects.

  Also added two clang-tidy checks : [performance-for-range-copy](https://releases.llvm.org/11.1.0/tools/clang/tools/extra/docs/clang-tidy/checks/performance-for-range-copy.html) and [performance-unnecessary-copy-initialization](https://releases.llvm.org/12.0.0/tools/clang/tools/extra/docs/clang-tidy/checks/performance-unnecessary-copy-initialization.html).

ACKs for top commit:
  vasild:
    ACK ae7ae36d31
  MarcoFalke:
    review ACK ae7ae36d31

Tree-SHA512: f6ac6b0cd0eee1e0c34d2f186484bc0f7ec6071451cccb33fa88a67d93d92b304e2fac378b88f087e94657745bca4e966dbc443759587400eb01b1f3061fde8c

src/test/validation_block_tests.cpp

@@ -183,7 +183,7 @@ BOOST_AUTO_TEST_CASE(processnewblock_signals_ordering)
             }
 
             // to make sure that eventually we process the full chain - do it here
-            for (auto block : blocks) {
+            for (const auto& block : blocks) {
                 if (block->vtx.size() == 1) {
                     bool processed = Assert(m_node.chainman)->ProcessNewBlock(block, true, &ignored);
                     assert(processed);