* feat: `settings.json` `encryption` is now string
* feat: api-compat for encryption in `settings.json`
* feat: rpc now uses the same strings as `settings.json` for encryption modes
* feat: api-compat for encryption in rpc
* code review: use `to_variant()`
* test: add TransmissionTest fixture that calls tr_lib_init()
* refactor: use std::call_once() in tr_lib_init()
* test: ensure quarks are sorted in RpcTest::sessionGet
* refactor: use ::libtransmission::test::TransmissionTest
prefer this over ::testing::Test to ensure tr_lib_init() is called once
* feat: sync the values of `preferred_transports` and `*_enabled`
* refactor: avoid using `tr_session::allowsTCP()`
* code review: implement fixup methods in source file
* feat: store `preferred_transports` as array in `settings.json`
* refactor: `Settings::save()` returns `tr_variant::Map`
* feat: new RPC API for `preferred_transports`
* feat: new arg `--preferred-transports` for remote
* test: new `tr_variant` API in `json-test.cc`
* test: new `tr_variant` API in `variant-test.cc`
* chore: housekeeping
* test: new `tr_variant` API in `dht-test.cc`
* fix: use `reinterpret_cast` in `tr_variant::make_raw()`
* fix: add missing `typename` in `tr_variant::make_raw()`
* test: new `tr_variant` API in `settings-test.cc`
* test: new `tr_variant` API in `move-test.cc`
* test: new `tr_variant` API in `rpc-test.cc`
* test: new `tr_variant` API in `makemeta-test.cc`
* test: new `tr_variant` API in `session-test.cc`
* refactor: move tr_preallocation_mode info tr_open_files
* refactor: remove unnecessary error nullptr check
* refactor: use snake_case for private method names in inout.cc
* refactor: extract-method get_fd() from read_or_write_bytes()
* refactor: make function args const where possible
* refactor: simplify read_or_write_bytes()
* refactor: make buflen a uint64_t in read_or_write_piece()
* refactor: move tr_torrentStop() logic from read_or_write_piece() to tr_ioWrite()
* refactor: make tr_ioFoo() functions take a const torrent
* refactor: make tr_cache::close_torrent_files() take a tor_id instead of a torrent
* Use imported CMake target for CURL
* Use imported CMake target for fmtlib
* Use imported CMake target for WideInteger
* Use imported CMake target for FastFloat
* Use imported CMake target for UtfCpp
* Use imported CMake target for Threads
* Use imported CMake target for Iconv
* Use imported CMake target for crypto backend
* Use imported CMake target for GTK
* Use imported CMake target for Qt
* Use imported CMake target for deflate
* Use imported CMake target for libevent
* Use imported CMake target for natpmp
* Use imported CMake target for miniupnpc
* Use imported CMake target for dht
* Use imported CMake target for psl
* Use imported CMake target for libutp
* Use imported CMake target for libb64
* Use include directories from libtransmission target
* fix: save log level, encryption mod, preallocation mode as ints
* fix: ensure log level is saved in tr_sessionGetSettings()
* fix: ensure the right verbosity row is selected
