Add versioned dev_requirements for py 3.8 3.9 3.10

Different version of python have different dev requirements. Previously,
`dev_requirements.txt` was generated for python3.8 and assumed to work
for other versions of python.

That was more or less a safe assumption, except is now causing problems.
Specifically, gtsam is not available on python 3.10, but we'd like to
add it as a dev requirement for python 3.8 and 3.9.

`symforce_requirements_test.py` cannot be run until symforce has been
installed, but one might reasonably want to `pip install -r
dev_requirements.txt` before installing symforce (to use the pinned
build depencies during installation).

To make this circular dependency less painful for the user, I'm adding
- `dev_requirements_38.txt`
- `dev_requirements_39.txt`
- `dev_requirements_310.txt`
so that the correct dev requirements can be installed before symforce
installation for any supported python version.

Modified `test/symforce_requirements_test.py` to only test/update the
`dev_requirements_XY.txt` of the python version being used.

Since the public CI is already running this test, it will guarentee that
none of these files will go out of date.

Needed to amend both ci.yml and docs.yml to use the correct
`dev_requirements_XY.txt`.

Also needed to update the `README.md` accordingly.

.github/workflows/ci.yml

@@ -75,7 +75,7 @@ jobs:
               libeigen3-dev
 
       - name: Install python dependencies
-        run: pip install -r dev_requirements.txt
+        run: pip install -r dev_requirements_$(${{ matrix.python }} -c 'import sys; print(f"{sys.version_info.major}{sys.version_info.minor}")').txt
 
       - name: Run cmake build
         run: |
@@ -87,14 +87,12 @@ jobs:
           cmake --build build -j $(nproc)
 
       # - lcmtypes need to be available for tests
-      # - Exact contents of dev_requirements.txt depend on python version. Need to update file to
-      # match current python version to avoid failure of corresponding gen test. symforce needs
-      # to be on the PYTHONPATH to run gen test in this manner.
+      # TODO(brad): Check that it is still necessary for $(pwd) to be on the PYTHONPATH
+      # - symforce needs to be on the PYTHONPATH to run gen test in this manner.
       - name: Run tests
         run: |
           pip install build/lcmtypes/python2.7
           export PYTHONPATH=$PYTHONPATH:$(pwd)
-          ${{ matrix.python }} test/symforce_requirements_test.py --update
           ctest --test-dir build -j $(nproc) || true
           ctest --test-dir build -j $(nproc) --rerun-failed --output-on-failure
 

.github/workflows/docs.yml

@@ -23,7 +23,7 @@ jobs:
             pandoc
 
       - name: Install python dependencies
-        run: pip install -r dev_requirements.txt
+        run: pip install -r dev_requirements_$(python3 -c 'import sys; print(f"{sys.version_info.major}{sys.version_info.minor}")').txt
 
       - name: Run cmake build
         run: |

README.md

@@ -565,7 +565,7 @@ pip install -e .
 
 This will build the C++ components of SymForce, but you won't be able to run `pip install -e .` repeatedly if you need to rebuild C++ code.  If you're changing C++ code and rebuilding, you should build with CMake directly as described <a href="#build-with-cmake">below</a>.
 
-`pip install .` will not install pinned versions of SymForce's dependencies, it'll install any compatible versions.  It also won't install all packages required to run all of the SymForce tests and build all of the targets (e.g. building the docs or running the linters).  If you want all packages required for that, you should `pip install .[dev]` instead (or one of the other groups of extra requirements in our `setup.py`).  If you additionally want pinned versions of our dependencies, which are the exact versions guaranteed by CI to pass all of our tests, you can install them from `pip install -r dev_requirements.txt`.
+`pip install .` will not install pinned versions of SymForce's dependencies, it'll install any compatible versions.  It also won't install all packages required to run all of the SymForce tests and build all of the targets (e.g. building the docs or running the linters).  If you want all packages required for that, you should `pip install .[dev]` instead (or one of the other groups of extra requirements in our `setup.py`).  If you additionally want pinned versions of our dependencies, which are the exact versions guaranteed by CI to pass all of our tests, you can install them from `pip install -r dev_requirements_XY.txt` (where `X` and `Y` are the major and minor versions of your python; e.g. `dev_requirements_38.txt` for python3.8).
 
 ## Build with CMake
 
@@ -574,8 +574,9 @@ SymForce into your Python environment, so you'll need to add it to your PYTHONPA
 
 Install python requirements:
 ```bash
-pip install -r dev_requirements.txt
+pip install -r dev_requirements_38.txt
 ```
+(or `dev_requirements_39.txt`/`dev_requirements_310.txt` for python3.9 and python3.10, respectively).
 
 Build SymForce (requires C++14 or later):
 ```bash