Release Candidate v3.10.9.0-rc1

Here is the git log for v3.10.9.0-rc1 ... we'll write up a nicer changelog for the final.

fix gr_python_install
UHD: set URL of FPGA FFT to avoid collision with plain URL
GRC: enable setting of documentation URLs, relative or absolute in yaml
fec: add FEC_API to CCSDS Reed-Solomon functions
blocks: Fix flaky chunk throttling test
blocks: msq_pair_to_var QA: wait up to 1 s.
qtgui: Remove unnecessary imports from templates
gr-uhd: Remove old references
analog: PLL frequency detector example: use limited-wait throttle
blocks: msg_pair_to_var: Log with block logger, not gr.log (#6950)
pmt: Disallow None for pmt_t arguments in Python
conda: sync conda-build.yml with main branch
qt-gui: QRfnocF15ColorMapper: Add missing <array> include.
MNT: Re-rendered with conda-build 3.27.0, conda-smithy 3.28.0, and conda-forge-pinning 2023.11.07.18.09.01
ci: conda: Move conda stuff to .conda directory to unify with OOT style.
ci: conda: Clean up recipe and update for latest boost packages.
modtool: template: Update conda recipe.
spdlog: include spdlog system settings header before including spdlog/fmt/
gr-qtgui: QT GUI Msg Push Button add callback for Message Value
Use pointers to pass s32fc arguments to VOLK
filter: Accept rounded output from fir_filter_fsf
Remove 'friend' from 'read_wavein' callback function (#6971)
gr-uhd: RFNoC Rx-Streamer: Add start stream options
grc: Extend ID blacklist by Python keywords
grc/core/FlowGraph: pythonify old strings, lists
grc: param.py: refactor internal function name
grc/core: Type annotations, so I can somewhat sensibly work in my editor
grc/core/FlowGraph: remove unused imports
grc/core/FlowGraph: refactor internal namespace refresh code
grc: remove Py3 backports
grc: no Python type 'long'
grc: backlist gnuradio as valid id
grc: use yaml.CSafeLoader for performance if available
GRC: generated python code use gr.logger.warn instead of ….warning
grc: Consistently format filenames in messages
uhd: rfnoc: Add back-edge property to RFNoC connections
grc: Add edge (connection) properties
grc: Check flow graph format version
grc: Remove superfluous import
fec: fix incorrect runtime error message
gr-fec: cc_decoder: untangle C-style, strange argument check
project: add tox.ini, so that editors use the same formatting as github CI
Python: minimum version 3.7.2, was 3.6.5
qtgui: remove stray d_wf_lines in rfnoc_f15_display
qtgui: Rename instances of fosphor to rfnoc_f15
Revert "qtgui: Add fosphor formatter block"
fosphor display widget: Fix std::bad_alloc
qtgui: conditionally install fosphor yaml files
qtgui/QFosphorColorMapper: std::sstream+string replacing sscanf("%m")+char*
uhd: Add RFNoC Fosphor example
qtgui: Add fosphor formatter block
qtgui: Add fosphor display widget
grc: Fix way-over-backslashing in file paths
gr-digital every time
grc: Remove param field colorings by type and replace with labels