Remove Boost.Coroutine dependency and old Coro API

Delete the old Boost.Coroutine-based Coro class and all supporting
infrastructure, now that all callers have been migrated to the C++20
CoroTaskRunner API:

- Delete include/xrpl/core/Coro.ipp (entire file)
- Remove class Coro, Coro_create_t, postCoro() from JobQueue.h
- Remove the large comment block explaining old Coro lifecycle
- Remove boost::coroutine from cmake COMPONENTS and link targets
- Remove Boost::context from cmake find_dependency (was only needed
  by Boost.Coroutine)
- Remove BOOST_COROUTINES_NO_DEPRECATION_WARNING compile definition
- Remove boost::coroutine from conanfile.py requirements

This completes the Boost.Coroutine → C++20 coroutines migration.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: pratikmankawde

cmake/XrplConfig.cmake

@@ -16,8 +16,6 @@ find_dependency(Boost
                 COMPONENTS
                 chrono
                 container
-                context
-                coroutine
                 date_time
                 filesystem
                 program_options

cmake/XrplInterface.cmake

@@ -22,7 +22,6 @@ target_compile_definitions(
               BOOST_FILESYSTEM_NO_DEPRECATED
               >
               $<$<NOT:$<BOOL:${boost_show_deprecated}>>:
-              BOOST_COROUTINES_NO_DEPRECATION_WARNING
               BOOST_BEAST_ALLOW_DEPRECATED
               BOOST_FILESYSTEM_DEPRECATED
               >

cmake/deps/Boost.cmake

@@ -4,7 +4,6 @@ include(XrplSanitizers)
 find_package(Boost REQUIRED
              COMPONENTS chrono
                         container
-                        coroutine
                         date_time
                         filesystem
                         json
@@ -21,7 +20,6 @@ target_link_libraries(
     INTERFACE Boost::headers
               Boost::chrono
               Boost::container
-              Boost::coroutine
               Boost::date_time
               Boost::filesystem
               Boost::json

conanfile.py

@@ -196,7 +196,6 @@ def package_info(self):
             "boost::headers",
             "boost::chrono",
             "boost::container",
-            "boost::coroutine",
             "boost::date_time",
             "boost::filesystem",
             "boost::json",