refactor!: Use uv to install python virtual env (#353)

#### Description of changes
Uses `uv` rather than `pip` to install the virtual environment in the
docker image. This should be transparent to users: the virtual
environment created at the end is the same.

On a test tesseract build, I observed the installation of dependencies
into the virtual env speed up by ~6x. There's another case I've run into
where pip is actually unable to resolve the dependencies and gets stuck;
I've been using this branch to get around that.

I referred to the following documentation page when making this change:
https://docs.astral.sh/uv/guides/integration/docker/

#### Testing done
- Added an example tesseract containing a custom `pip install` build
step and corresponding test case
- Manual testing: I've been using this patch for my own tesseract builds
for about a month, and seen no issues.

---------

Co-authored-by: Alessandro Angioi <alessandro.angioi@simulation.science>

Author: johnbcoughlin

examples/pip_custom_step/tesseract_api.py

@@ -0,0 +1,17 @@
+# Copyright 2025 Pasteur Labs. All Rights Reserved.
+# SPDX-License-Identifier: Apache-2.0
+
+from pydantic import BaseModel, Field
+
+
+class InputSchema(BaseModel):
+    name: str = Field(description="Name of the person you want to greet.")
+
+
+class OutputSchema(BaseModel):
+    greeting: str = Field(description="A greeting!")
+
+
+def apply(inputs: InputSchema) -> OutputSchema:
+    """Greet a person whose name is given as input."""
+    return OutputSchema(greeting=f"Hello {inputs.name}!")

examples/pip_custom_step/tesseract_config.yaml

@@ -0,0 +1,23 @@
+name: "helloworld"
+version: "1.0.0"
+description: "A sample Python app"
+
+build_config:
+  # Base image to use for the container, must be Ubuntu or Debian-based
+  # base_image: "debian:bookworm-slim"
+
+  # Platform to build the container for. In general, images can only be executed
+  # on the platform they were built for.
+  # target_platform: "native"
+
+  # Additional packages to install in the container (via apt-get)
+  # extra_packages:
+  #  - package_name
+
+  # Data to copy into the container, relative to the project root
+  # package_data:
+  #  - [path/to/source, path/to/destination]
+
+  # Additional Dockerfile commands to run during the build process
+  custom_build_steps:
+   - RUN pip install numpy

examples/pip_custom_step/tesseract_requirements.txt

@@ -0,0 +1,2 @@
+# Add Python requirements like this:
+# numpy==1.18.1

examples/vectoradd_torch/tesseract_requirements.txt

@@ -1 +1,2 @@
-torch --index-url https://download.pytorch.org/whl/cpu
+--index-url https://download.pytorch.org/whl/cpu
+torch

tesseract_core/sdk/templates/Dockerfile.base

@@ -5,6 +5,11 @@ FROM {{ config.build_config.base_image }} AS build_stage
 FROM --platform={{ config.build_config.target_platform }} {{ config.build_config.base_image }} AS build_stage
 {% endif %}
 
+# Obtain uv and companions
+COPY --from=ghcr.io/astral-sh/uv:latest /uv /uvx /bin/
+
+ENV UV_LINK_MODE=copy
+
 # Install Python if necessary
 RUN if [ ! -x "$(command -v python3)" ]; then \
     apt-get update && apt-get install -y --no-install-recommends \
@@ -40,7 +45,7 @@ COPY local_requirements/ ./local_requirements
 
 # Build a python venv from python provider build scripts.
 # The build script has to create a venv at /python-env
-RUN {% if use_ssh_mount %}--mount=type=ssh{% endif %} bash {{ config.build_config.requirements._build_script }}
+RUN --mount=type=cache,target=/root/.cache/uv {% if use_ssh_mount %}--mount=type=ssh{% endif %} bash {{ config.build_config.requirements._build_script }}
 ENV PATH="/python-env/bin:$PATH"
 
 # Stage 2: Set up runtime environment

tesseract_core/sdk/templates/build_pip_venv.sh

@@ -2,9 +2,7 @@
 
 set -e  # Exit immediately if a command exits with a non-zero status
 
-python3 -m venv /python-env
-
-# Activate virtual environment
+uv venv /python-env
 source /python-env/bin/activate
 
 # Collect dependencies
@@ -14,7 +12,7 @@ TESSERACT_DEPS=$(find ./local_requirements/ -mindepth 1 -maxdepth 1 2>/dev/null
 TESSERACT_DEPS+=" -r tesseract_requirements.txt"
 
 # Install dependencies
-pip install $TESSERACT_DEPS
+uv -v pip install --compile-bytecode $TESSERACT_DEPS
 
 # HACK: If `tesseract_core` is part of tesseract_requirements.txt, it may install an incompatible version
 # of the runtime from PyPI. We remove the runtime folder and install the local version instead.
@@ -23,4 +21,7 @@ if [ -d "$runtime_path" ]; then
     rm -rf "$runtime_path"/runtime
 fi
 
-pip install ./tesseract_runtime
+uv -v pip install --compile-bytecode ./tesseract_runtime
+
+# Install pip itself into the virtual environment for use by any custom build steps
+uv pip install pip

tests/endtoend_tests/test_examples.py

@@ -107,6 +107,16 @@ class Config:
             ),
         ],
     ),
+    "pip_custom_step": Config(
+        test_with_random_inputs=True,
+        sample_requests=[
+            SampleRequest(
+                endpoint="apply",
+                payload={"inputs": {"name": "Ozzy"}},
+                output_contains_pattern="Hello Ozzy!",
+            ),
+        ],
+    ),
     "pyvista-arm64": Config(
         test_with_random_inputs=True,
         sample_requests=[