moving FAST_CI_MODE flag to pytest script (#1111)

### Description

Moving FAST_CI_MODE flag to related pytest script file to avoid future
lack of compatibility between the setup between Jenkins or GitHub CI

### Type of changes

<!-- Mark the relevant option with an [x] -->

- [ ] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [x] Refactor
- [ ] Documentation update
- [ ] Other (please describe):

### CI Pipeline Configuration

Configure CI behavior by applying the relevant labels:

-
[SKIP_CI](https://github.com/NVIDIA/bionemo-framework/blob/main/docs/docs/user-guide/contributing/contributing.md#skip_ci)
- Skip all continuous integration tests
-
[INCLUDE_NOTEBOOKS_TESTS](https://github.com/NVIDIA/bionemo-framework/blob/main/docs/docs/user-guide/contributing/contributing.md#include_notebooks_tests)
- Execute notebook validation tests in pytest
-
[INCLUDE_SLOW_TESTS](https://github.com/NVIDIA/bionemo-framework/blob/main/docs/docs/user-guide/contributing/contributing.md#include_slow_tests)
- Execute tests labelled as slow in pytest for extensive testing

> [!NOTE]
> By default, the notebooks validation tests are skipped unless
explicitly enabled.

#### Authorizing CI Runs

We use
[copy-pr-bot](https://docs.gha-runners.nvidia.com/apps/copy-pr-bot/#automation)
to manage authorization of CI
runs on NVIDIA's compute resources.

- If a pull request is opened by a trusted user and contains only
trusted changes, the pull request's code will
automatically be copied to a pull-request/ prefixed branch in the source
repository (e.g. pull-request/123)
- If a pull request is opened by an untrusted user or contains untrusted
changes, an NVIDIA org member must leave an
`/ok to test` comment on the pull request to trigger CI. This will need
to be done for each new commit.

### Usage

<!--- How does a user interact with the changed code -->

```python
# TODO: Add code snippet
```

### Pre-submit Checklist

<!--- Ensure all items are completed before submitting -->

- [ ] I have tested these changes locally
- [ ] I have updated the documentation accordingly
- [ ] I have added/updated tests as needed
- [ ] All existing tests pass successfully


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

* **Chores**
* Streamlined CI configuration for notebook tests by moving fast-mode
environment handling into the test script and removing redundant
settings from the workflow.
* **Tests**
* Consolidated environment setup for notebook pytest runs to improve
consistency and reliability in CI.
  
No user-facing changes or impact on product behavior.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Author: dorotat-nv

.github/workflows/unit-tests-framework.yml

@@ -239,8 +239,6 @@ jobs:
       - name: Run notebook tests
         env:
           BIONEMO_DATA_SOURCE: ngc
-          # this variable should be used in the notebooks to run a subset of the model layers or a smaller model/dataset
-          FAST_CI_MODE: true
         run: |
           chmod +x ./ci/scripts/run_pytest_notebooks.sh
           ./ci/scripts/run_pytest_notebooks.sh

ci/scripts/run_pytest_notebooks.sh

@@ -19,4 +19,4 @@
 # Enable strict mode with better error handling
 set -euox pipefail
 
-pytest -v --nbval-lax -x -p no:python docs/ sub-packages/
+FAST_CI_MODE=true pytest -v --nbval-lax -x -p no:python docs/ sub-packages/