Drop Levanter protobuf upper bound (#5171)

## Summary

- Drop Levanter's direct `protobuf<7` upper bound now that
TensorBoard/XProf compatibility has been rechecked.
- Refresh the lockfile for the affected profiling packages.

Fixes #5139.

## Validation

- `uv lock -P protobuf -P tensorboard -P tensorboardx -P xprof`
- `uv run --package marin-levanter --extra profiling --group test pytest
lib/levanter/tests/test_tensorboard.py`
- `uv run --isolated --with 'protobuf>=7' --with 'tensorboard>=2.16'
--with 'tensorboardX>=2.6' --with 'xprof' python -c "..."`
- `./infra/pre-commit.py --fix lib/levanter/pyproject.toml uv.lock`
- `uv lock --check`
- `git diff --check`

Co-authored-by: Romain Yon <1596570+yonromai@users.noreply.github.com>

Author: yonromai

lib/levanter/pyproject.toml

@@ -70,7 +70,7 @@ dependencies = [
     "deepdiff>=8.6.2",
     "lenses",
     "jinja2",  # needed for apply_chat_template
-    "protobuf>=6,<7",  # ensure TB/XProf compatibility
+    "protobuf>=6",
     "immutabledict",
 ]