langchain-google-vertexai's pyarrow<24.0.0 conflicts with projects needing pyarrow 25

### Package (Required)

- [ ] langchain-google-genai
- [x] langchain-google-vertexai
- [ ] langchain-google-community
- [ ] Other / not sure / general

### Checked other resources

- [x] I added a descriptive title to this issue
- [x] I searched the LangChain documentation and API reference (linked above)
- [x] I used the GitHub search to find a similar issue and didn't find it
- [x] I am sure this is a bug and not a question or request for help

### Example Code (Python)

```python
[project]
name = "repro"
version = "0.1.0"
requires-python = ">=3.13"
dependencies = [
    "langchain-google-vertexai>=3.2.4",
    "pyarrow>=25.0.1",
]

Then `uv lock`.
```

### Error Message and Stack Trace (if applicable)

```shell
× No solution found when resolving dependencies:
  ╰─▶ Because langchain-google-vertexai>=3.2.4 depends on
      pyarrow>=19.0.1,<24.0.0 and your project depends on
      langchain-google-vertexai>=3.2.4, we can conclude that your project
      depends on pyarrow>=19.0.1,<24.0.0.
      And because your project depends on pyarrow>=25.0.1, we can conclude
      that your project's requirements are unsatisfiable.
```

### Description

We ran into this in a monorepo where several services share an internal library. One service uses `langchain-google-vertexai`; another reads Parquet and needs pyarrow 25. Because the shared library declares `pyarrow`, vertexai's `<24.0.0` cap holds it back and the two can't coexist.

As far as I can tell vertexai is the only package in the tree that requires pyarrow, and doesn't import it directly – I assume it's there for the optional pyarrow paths in `google-cloud-bigquery` / `google-cloud-aiplatform`, which don't set an upper bound themselves.

Would you consider bumping the ceiling to `<26.0.0`?

**Environment:** Python 3.13 · langchain-google-vertexai 3.2.4 · uv 0.12.5

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