refactor: simplify command execution and remove PTY handling (#1641)

# What does this PR do?

A PTY is unnecessary for interactive mode since `subprocess.run()`
already inherits the calling terminal’s stdin, stdout, and stderr,
allowing natural interaction. Using a PTY can introduce unwanted side
effects like buffering issues and inconsistent signal handling. Standard
input/output is sufficient for most interactive programs.

This commit simplifies the command execution by:

1. Removing PTY-based execution in favor of direct subprocess handling
2. Consolidating command execution into a single run_command function
3. Improving error handling with specific subprocess error types
4. Adding proper type hints and documentation
5. Maintaining Ctrl+C handling for graceful interruption

## Test Plan

```
llama stack run
```

Signed-off-by: Sébastien Han <seb@redhat.com>

.github/workflows/integration-tests.yml

@@ -56,8 +56,7 @@ jobs:
           INFERENCE_MODEL: "meta-llama/Llama-3.2-3B-Instruct"
         run: |
           source .venv/bin/activate
-          # TODO: use "llama stack run"
-          nohup uv run python -m llama_stack.distribution.server.server --yaml-config ./llama_stack/templates/ollama/run.yaml > server.log 2>&1 &
+          nohup uv run llama stack run ./llama_stack/templates/ollama/run.yaml --image-type venv > server.log 2>&1 &
 
       - name: Wait for Llama Stack server to be ready
         run: |

.github/workflows/providers-build.yml

@@ -40,6 +40,7 @@ jobs:
       matrix:
         template: ${{ fromJson(needs.generate-matrix.outputs.templates) }}
         image-type: [venv, container]
+      fail-fast: false # We want to run all jobs even if some fail
 
     steps:
       - name: Checkout repository
@@ -67,7 +68,9 @@ jobs:
 
       - name: Run Llama Stack Build
         run: |
-          uv run llama stack build --template ${{ matrix.template }} --image-type ${{ matrix.image-type }} --image-name test
+          # USE_COPY_NOT_MOUNT is set to true since mounting is not supported by docker buildx, we use COPY instead
+          # LLAMA_STACK_DIR is set to the current directory so we are building from the source
+          USE_COPY_NOT_MOUNT=true LLAMA_STACK_DIR=. uv run llama stack build --template ${{ matrix.template }} --image-type ${{ matrix.image-type }} --image-name test
 
       - name: Print dependencies in the image
         if: matrix.image-type == 'venv'