Remove `dataset` keyword from code base and use keyword `asset`

### Task Summary

### **Title: Refactor `dataset` to generalized `asset` concept to support new resource types**

#### **Context**
Currently in Texera, we use the keyword `dataset` to represent a group of files a user has uploaded into a LakeFS repository. Essentially, a `dataset` acts as a file system. This concept is heavily coupled throughout our stack: it functions as a resource in the dashboard, defines types and structures during workflow execution, and serves as a direct reference point within UDFs and Python code.

#### **Motivation**
We are planning to introduce a new resource type called `model`. Under the hood, a `model` is architecturally identical to a `dataset`: it is simply a repository containing files and folders in a tree structure (similar to an S3 bucket), backed by LakeFS and MinIO.

Because models and datasets share the exact same underlying `file-system` storage mechanism, the interpretation of the files stored in MinIO should be decoupled from the storage structure itself. Instead, the reading process (e.g., a UDF operator reading a file as a binary) should dictate how the content is interpreted.

#### **Proposed Solution**
To generalize our current LakeFS/MinIO storage architecture to support both `datasets` and `models`, we need to refactor the codebase to use a broader abstraction.

We propose introducing a new core keyword: **`asset`**.
The `asset` concept will act as the universal pointer to our storage layer, encompassing various specific resource types, including both `dataset` and `model`.

#### **Tasks & Acceptance Criteria**
To implement this abstraction, we need to replace occurrences of `dataset` with the generalized `asset` keyword across the stack.

- [ ] **Database:** Rename all `dataset` occurrences in Postgres table names.
- [ ] **Common Utilities:** Update all storage utilities in the `common` directory that currently refer to `dataset`.
- [ ] **File Service:** Refactor all files within `file-service` to use the `asset` terminology.
- [ ] **UDF Definitions:** Update UDF classes and type definitions that currently hardcode `dataset` as the sole reference to storage.

### Priority

P2 – Medium

### Task Type

- [x] Code Implementation
- [ ] Documentation
- [x] Refactor / Cleanup
- [x] Testing / QA
- [x] DevOps / Deployment