Add actor library which implements the Actor model (see  https://en.wikipedia.org/wiki/Actor_model).

Implement run-to-completion for processSlotTX. This is achieved by using a new
dynamic_barrier_t which allows to specify callback after the first join has been
made.

This commit introduces dynamic_barrier_t. Its a thread barrier that counts joins
but allows callback to be specified later. See std::barrier for a basic barrier
description.

Added support for NTN FDD FR1 bands 254, 255, 256 as specified in 3GPP TS 38.101-5
Conf files added for 15Khz, 5Mhz and 30Khz, 10Mhz configurations added for these bands

telnetsrv uses the Intel/AMD-specific "cpuid" instruction, which is not
available on ARM machines. Remove the call.

The previous code was checking for the number of cores, which is
retained by a call to get_nprocs(). I did not find an equivalent for the
number of threads in C. In C++, there would be
https://en.cppreference.com/w/cpp/thread/thread/hardware_concurrency, in
case it's relevant for anybody.

This changes the way T_IDs are defined. The T_ID macro was using a integer to pointer cast in
order to provide type safety. This trick disables some compiler optimizations, as explained
here: https://clang.llvm.org/extra/clang-tidy/checks/performance/no-int-to-ptr.html.
Removing the type cast reenables the compiler optimizations.

Since long long is the bigger type ( 8 bytes ) of the two used ( long long and uint32_t ),
and long long is also available on ARM, change this parameter to always have this type.

This allows to always use format specifier '%lld' in the logs that use TICK_TO_US, which would otherwise return long long or uint32_t depending on architecture.

CodeChecker is a python application that collects reports from static analyzers like
clang-tidy, clangsa, cppcheck.

* abort generates a core dump

allocating enough memory to hold url to index page.

Some people needed that.

Let's stop to 19 for the time being. It's tricky enough.
We can increase later if needed. (A previous commit
made the tracers to accept up to 32 variables.)

80 columns are enough.

T_MAX_ARGS was 16 and some people start to use the T machinery with
more than 16 values. So be it. Let tracers be friendly and accept 32.
(More commits to follow for full support.)

Also why is T_MAX_ARGS in T_defs.h when it's only used by event.h?
Hum?

Pass consistently the NR_timer_t object through a pointer. Since we have
to modify all occurrences of is_nr_timer_active(), we use that occasion
and rename that function to nr_timer_is_active() to make it consistent
with all other functions, starting with nr_timer.

A new phy scope based on ImGui and ImPlot. This scope uses a different concurrency model than previous
scopes.

The PHY thread writing the data first checks if the data is ready to be written. If its not, nothing is copied.
The GUI thread reads data if available and marks it ready to write. This makes sure that the PHY threads are not
busy copying data that would never be displayed.

Some of the scopes also have a freeze functionality that further limit the amount of data that needs to be copied
from PHY threads. If a scope is "frozen" it still allows the user to explore the data using plots zoom/pan functions
but doesn't cause PHY threads to perform extra writes on the displayed data.

A compile option was added to enable/disable the scope. Use cmake -DENABLE_IMSCOPE=ON to enable the scope.

Update CXX standard to 17; it is required by some libraries (e.g., dear imgui). The oldest gcc version in
use by a distribution supported is Ubuntu 20, which has gcc 9.4 with c++17 support.