feat: planner client and pressure reconciler with unit tests

[cbartz]

Applicable spec: ISD-244

Overview

PR to add pressure_reconciler on the github-runner manager application side.

To allow easier review, the functionality to use the planner is split into multiple PRs. Follow-up PR's to add using it in the charm and integration tests are expected.

The PR is based on the work in #705

Rationale

In order to use the planner, we need to add support to the github-runner-manager application.

Juju Events Changes

n/a

Module Changes

• PlannerClient for communicating with the planner service
• PressureReconciler for scaling runners based on pressure signals
• Configuration fields for planner URL and token
• Unit tests for both components

Library Changes

n/a

Checklist

• The charm style guide was applied.
• The contributing guide was applied.
• The changes are compliant with ISD054 - Managing Charm Complexity
• The documentation for charmhub is updated.
• The PR is tagged with appropriate label (urgent, trivial, complex).
• The changelog is updated with changes that affects the users of the charm.
• The application version number is updated in github-runner-manager/pyproject.toml.

[Copilot]

Pull request overview

This PR adds infrastructure for planner-based runner scaling to the github-runner-manager application. The implementation introduces a PlannerClient for communicating with an external planner service, and a PressureReconciler that uses pressure signals from the planner to scale runners up or down. The changes are designed to be integrated into the charm in follow-up PRs.

Changes:

• Added PlannerClient for HTTP communication with the planner service, including flavor retrieval and pressure streaming
• Added PressureReconciler that runs create/delete loops to maintain desired runner count based on planner pressure
• Extended ApplicationConfiguration with optional planner_url and planner_token fields
• Added comprehensive unit tests for both new components

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 11 comments.

Show a summary per file

File	Description
github-runner-manager/src/github_runner_manager/planner_client.py	New HTTP client for planner service with flavor and pressure streaming support
github-runner-manager/src/github_runner_manager/manager/pressure_reconciler.py	New reconciler implementing planner-driven scaling with separate create/delete loops
github-runner-manager/src/github_runner_manager/configuration/base.py	Added optional planner_url and planner_token configuration fields
github-runner-manager/src/github_runner_manager/manager/runner_manager.py	Enhanced delete_runners docstring to clarify deletion behavior
github-runner-manager/tests/unit/test_planner_client.py	Unit tests for PlannerClient with mocked HTTP responses
github-runner-manager/tests/unit/test_pressure_reconciler.py	Unit tests for PressureReconciler covering error handling and reconciliation logic
github-runner-manager/tests/unit/test_config.py	Added tests for optional planner configuration fields
github-runner-manager/tests/unit/test_runner_scaler.py	Updated fixture to include planner configuration
github-runner-manager/pyproject.toml	Bumped version from 0.12.0 to 0.13.0

[florentianayuwono]

very neat and easy to read, thanks for the pr chris!