Upstreamed the fine-grained parallel router implementation into the VTR
master. The original branch is https://github.com/verilog-to-routing/vtr-verilog-to-routing/tree/mq-parallel-router.

Modified the MultiQueue (SPAA'24) implementation and integrated it into
the VTR codebase.

The original FG parallel router used to use boost. VTR does not install
boost by default. Moved to STL instead.

Added a partial abstract class for ConnectionRouter, derived from the
pure abstract ConnectionRouterInterface.

The SerialConnectionRouter and ParallelConnectionRouter classes are now
derived from the ConnectionRouter class, utilizing the common class
members and helper functions to reduce code duplication.

Added Doxygen-style code comments and documentation for connection
routers, including the ConnectionRouter abstract class, the Parallel-
ConnectionRouter concrete class, and the SerialConnectionRouter concrete
class.

Updated the helper messages for command-line options added for parallel
connection router.

Fixed the interface issues of ConnectionRouter in NestedNetlistRouter.

Fixed code formats.

Fixed typo in read_options.cpp.

Updated the command-line usage for parallel connection router in both
Read the Docs and read_options.cpp.

Added regression tests for parallel connection router by appending extra
sets of configurations to those VTR flow regression tests previously
selected by Fahri for testing coarse-grained parallel router.

Removed VPR connection router test (vpr/test/test_connection_router.cpp),
since it has been out-dated for a very long time and has caused lots of
trouble for running VPR C++ tests locally.

Fixed a weird code formatting issue in libs/librtlnumber/src/include/
internal_bits.hpp. GitHub CI said the file failed dev/check-format.sh,
however, the same script runs perfectly in my local environment. Double
checked the version of clang-format, which seemed to be the same as CI.

Directly copied the file from the GitHub repo to resolve this issue.

The `No source in route tree` bug in ParallelConnectionRouter (since
commit 875b98e) has been fixed. It turns out that putting another member
variable `MultiQueueDAryHeap<HeapImplementation::arg_D> heap_` in the
derived class ParallelConnectionRouter together with the existing
`HeapImplementation heap_` in the base class ConnectionRouter causes the
issue. The solution is to keep `heap_` only in the base class and use
`ConnectionRouter<MultiQueueDAryHeap<HeapImplementation::arg_D>>` rather
than `ConnectionRouter<HeapImplementation>` for deriving the parallel
connection router.

Please note that ParallelConnectionRouter still has some bugs (i.e.,
getting stuck in the MultiQueue pop). This commit is not fully working.
Please do not use it for any experiments.

Updated the previously incorrect command-line options for the parallel
connection router in the regression tests.

Fixed the weird bug in parallel connection router as mentioned in commit
f73212c. The bug occurred because two function parameters 'num_threads'
and 'num_queues' have been misplaced when instantiating the MQ_IO. This
took two weeks to figure out exactly.

The VTR benchmark (`vtr_reg_qor_chain` task) has been tested/passed for
different cases (1) 'serial mode' 1T+2Q (1 thread, 2 queues), (2) 2T+4Q,
and (3) 4T+2Q.

The determinism has also been verified for the VTR benchmark.

Added more explanation to the command-line options messages and code
comments.

Cleaned up ParallelConnectionRouter-related codebase.

Updated the golden results for CI tests for parallel connection router:
 - `vtr_reg_strong/koios_test`
 - `vtr_reg_strong/strong_flat_router`
 - `vtr_reg_strong/strong_multiclock`
 - `vtr_reg_strong/strong_timing`