Remove taskchampion source from this repo (#3427)

* move taskchampion-lib to src/tc/lib, remove the rest
* update references to taskchampion
* Use a top-level Cargo.toml so everything is consistent
* apply comments from ryneeverett

src/columns/CMakeLists.txt

@@ -2,10 +2,10 @@ cmake_minimum_required (VERSION 3.22)
 include_directories (${CMAKE_SOURCE_DIR}
                      ${CMAKE_SOURCE_DIR}/src
                      ${CMAKE_SOURCE_DIR}/src/tc
+                     ${CMAKE_SOURCE_DIR}/src/tc/lib
                      ${CMAKE_SOURCE_DIR}/src/commands
                      ${CMAKE_SOURCE_DIR}/src/columns
                      ${CMAKE_SOURCE_DIR}/src/libshared/src
-                     ${CMAKE_SOURCE_DIR}/taskchampion/lib
                      ${TASK_INCLUDE_DIRS})
 
 set (columns_SRCS Column.cpp Column.h