requirements: update fastkde requirement

Updates the requirements on [fastkde](https://github.com/LBL-EESA/fastkde) to permit the latest version.
- [Release notes](https://github.com/LBL-EESA/fastkde/releases)
- [Commits](LBL-EESA/fastkde@v1.0.24...v2.1.3)

---
updated-dependencies:
- dependency-name: fastkde
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

requirements.txt

@@ -1,6 +1,6 @@
 beartype<0.20.0
 dill<0.3.10
-fastkde>=1.0.24, <1.0.31
+fastkde>=1.0.24, <2.1.4
 graph-scheduler>=1.2.1, <1.3.0
 graphviz<0.21.0
 grpcio<1.68.0