fix(libstore-tests): remove use-after-free bug for StringSource (backport #11813)

[mergify]

Unfortunately StringSource class is very easy was very easy to misuse because the ctor took a plain std::string_view which has a bad habit of being implicitly convertible from an rvalue std::string. This lead to unintentional use-after-free bugs.

This patch makes StringSource much harder to misuse by disabling the ctor from a std::string && (but const std::string & is ok).

Fix affected tests from libstore-tests.
Reformat those tests with clangd's range formatting since the diff is tiny and it seems appropriate.

Motivation

Ran some tests under ASAN and UBSAN and got shocked by the amount of errors. This looks a good starting point for starting to untangle them.

Context

For reference here's the ASAN log for one of the two tests:

==3145773==ERROR: AddressSanitizer: stack-use-after-scope on address 0x7fffdbca8500 at pc 0x7ffff7993882 bp 0x7ffffffeffb0 sp 0x7ffffffef770
READ of size 1 at 0x7fffdbca8500 thread T0
    #0 0x7ffff7993881 in __interceptor_memcpy (/nix/store/40yjzm7r5ki59kkk9423dnwbm86x7pyd-gcc-13.2.0-lib/lib/libasan.so.8+0x71881)
    #1 0x7fffe3d752cb in std::char_traits<char>::copy(char*, char const*, unsigned long) /nix/store/fg7ass3a5m5pgl26qzfdniicbwbgzccy-gcc-13.2.0/include/c++/13.2.0/bits/char_traits.h:445
    #2 0x7fffe3d752cb in std::char_traits<char>::copy(char*, char const*, unsigned long) /nix/store/fg7ass3a5m5pgl26qzfdniicbwbgzccy-gcc-13.2.0/include/c++/13.2.0/bits/char_traits.h:437
    #3 0x7fffe3d752cb in std::basic_string_view<char, std::char_traits<char> >::copy(char*, unsigned long, unsigned long) const /nix/store/fg7ass3a5m5pgl26qzfdniicbwbgzccy-gcc-13.2.0/include/c++/13.2.0/string_view:327
    #4 0x7fffe3d752cb in nix::StringSource::read(char*, unsigned long) ../src/libutil/serialise.cc:192
    #5 0x7fffe3d59cbf in nix::Source::operator()(char*, unsigned long) ../src/libutil/serialise.cc:81
    #6 0x7fffeeab3596 in unsigned int nix::readNum<unsigned int>(nix::Source&) ../src/libutil/serialise.hh:415
    #7 0x7fffef710339 in nix::readInt(nix::Source&) ../src/libutil/serialise.hh:428
    #8 0x7fffef710339 in nix::WorkerProto::BasicClientConnection::handshake(nix::BufferedSink&, nix::Source&, unsigned int, std::set<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::less<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > > const&) ../src/libstore/worker-protocol-connection.cc:168
    #9 0xd538b8 in operator() ../src/libstore-tests/worker-protocol.cc:733
    #10 0xd538b8 in readTest<nix::WorkerProtoTest_handshake_client_truncated_replay_throws_Test::TestBody()::<lambda(std::string)> > ../src/libutil-test-support/tests/characterization.hh:61
    #11 0xd538b8 in nix::WorkerProtoTest_handshake_client_truncated_replay_throws_Test::TestBody() ../src/libstore-tests/worker-protocol.cc:725
    #12 0x7ffff788125c in void testing::internal::HandleExceptionsInMethodIfSupported<testing::Test, void>(testing::Test*, void (testing::Test::*)(), char const*) (/nix/store/8br7fhn6qdrqm9f1acn35zadn0jrmlg9-gtest-1.14.0/lib/libgtest.so.1.14.0+0x6025c)
    #13 0x7ffff786806d in testing::Test::Run() (/nix/store/8br7fhn6qdrqm9f1acn35zadn0jrmlg9-gtest-1.14.0/lib/libgtest.so.1.14.0+0x4706d)
    #14 0x7ffff7868224 in testing::TestInfo::Run() (/nix/store/8br7fhn6qdrqm9f1acn35zadn0jrmlg9-gtest-1.14.0/lib/libgtest.so.1.14.0+0x47224)
    #15 0x7ffff7868456 in testing::TestSuite::Run() (/nix/store/8br7fhn6qdrqm9f1acn35zadn0jrmlg9-gtest-1.14.0/lib/libgtest.so.1.14.0+0x47456)
    #16 0x7ffff78779e6 in testing::internal::UnitTestImpl::RunAllTests() (/nix/store/8br7fhn6qdrqm9f1acn35zadn0jrmlg9-gtest-1.14.0/lib/libgtest.so.1.14.0+0x569e6)
    #17 0x7ffff786865a in testing::UnitTest::Run() (/nix/store/8br7fhn6qdrqm9f1acn35zadn0jrmlg9-gtest-1.14.0/lib/libgtest.so.1.14.0+0x4765a)
    #18 0x7ffff789e0bf in main (/nix/store/8br7fhn6qdrqm9f1acn35zadn0jrmlg9-gtest-1.14.0/lib/libgtest_main.so.1.14.0+0x10bf)
    #19 0x7fffdebe610d in __libc_start_call_main (/nix/store/87848rvrg5c7jmplpi0iapvbxyj9kfid-glibc-2.39-52/lib/libc.so.6+0x2a10d) (BuildId: 74e5f374333670d3fbe07e0abb58717eeababaa6)
    #20 0x7fffdebe61c8 in __libc_start_main_alias_1 (/nix/store/87848rvrg5c7jmplpi0iapvbxyj9kfid-glibc-2.39-52/lib/libc.so.6+0x2a1c8) (BuildId: 74e5f374333670d3fbe07e0abb58717eeababaa6)
    #21 0x4fedc4 in _start (nix/build/src/libstore-tests/nix-store-tests+0x4fedc4) (BuildId: 5ae976e9c97622accddce7010abbfe9dff93178b)

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This is an automatic backport of pull request #11813 done by [Mergify](https://mergify.com).