[docs] Move fine-grained-cache out of misc into incremental group

[wyattscarpenter]

It seems to belong better here, being related to this subject.

I also write down that it can only be seen in dmypy (this is the meaning of if server_options)

There are no tests; I manually verified this in normal mypy and dmypy

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

AutoSplit (https://github.com/Toufool/AutoSplit)
-   File "/tmp/mypy_primer/mypy_old/venv/bin/mypy", line 7, in <module>
+   File "/tmp/mypy_primer/mypy_new/venv/bin/mypy", line 7, in <module>
-   File "/tmp/mypy_primer/mypy_old/venv/lib/python3.13/site-packages/mypy/__main__.py", line 15, in console_entry
+   File "/tmp/mypy_primer/mypy_new/venv/lib/python3.13/site-packages/mypy/__main__.py", line 15, in console_entry
-   File "/tmp/mypy_primer/mypy_old/venv/lib/python3.13/site-packages/mypy/main.py", line 127, in main
+   File "/tmp/mypy_primer/mypy_new/venv/lib/python3.13/site-packages/mypy/main.py", line 127, in main
-   File "/tmp/mypy_primer/mypy_old/venv/lib/python3.13/site-packages/mypy/main.py", line 211, in run_build
+   File "/tmp/mypy_primer/mypy_new/venv/lib/python3.13/site-packages/mypy/main.py", line 211, in run_build
-   File "/tmp/mypy_primer/mypy_old/venv/lib/python3.13/site-packages/mypy/build.py", line 196, in build
+   File "/tmp/mypy_primer/mypy_new/venv/lib/python3.13/site-packages/mypy/build.py", line 196, in build
-   File "/tmp/mypy_primer/mypy_old/venv/lib/python3.13/site-packages/mypy/build.py", line 272, in _build
+   File "/tmp/mypy_primer/mypy_new/venv/lib/python3.13/site-packages/mypy/build.py", line 272, in _build
-   File "/tmp/mypy_primer/mypy_old/venv/lib/python3.13/site-packages/mypy/build.py", line 2946, in dispatch
+   File "/tmp/mypy_primer/mypy_new/venv/lib/python3.13/site-packages/mypy/build.py", line 2946, in dispatch
-   File "/tmp/mypy_primer/mypy_old/venv/lib/python3.13/site-packages/mypy/build.py", line 3346, in process_graph
+   File "/tmp/mypy_primer/mypy_new/venv/lib/python3.13/site-packages/mypy/build.py", line 3346, in process_graph
-   File "/tmp/mypy_primer/mypy_old/venv/lib/python3.13/site-packages/mypy/build.py", line 3475, in process_stale_scc
+   File "/tmp/mypy_primer/mypy_new/venv/lib/python3.13/site-packages/mypy/build.py", line 3475, in process_stale_scc
-   File "/tmp/mypy_primer/mypy_old/venv/lib/python3.13/site-packages/mypy/build.py", line 2493, in write_cache
+   File "/tmp/mypy_primer/mypy_new/venv/lib/python3.13/site-packages/mypy/build.py", line 2493, in write_cache
-   File "/tmp/mypy_primer/mypy_old/venv/lib/python3.13/site-packages/mypy/cache.py", line 28, in __init__
+   File "/tmp/mypy_primer/mypy_new/venv/lib/python3.13/site-packages/mypy/cache.py", line 28, in __init__