Add bisection state manager script

[justice-adams-apple]

• Add bisect.py

this python script is responsible for managing a repository bisection in a CI job. It is intended to be used in CI to keep track of a bisection process. This bisection manager orchestrates automated git bisections across CI/CD systems (Jenkins, GitHub Actions), manages bisection state, and generates comprehensive reports. By extracting the logic maintaining the binary search to a separate maintainable tool, we can eliminate much of that logic from the CI jobs themselves thus making this portable across CI systems.

This script runs the following commands:

• init: Initialize a new bisection session or continue an existing one. Outputs a JSON state object with session details, commit range, and first commit to test. Creates bisection_state.json, bisection.log, and restart_instructions.log to be archived by CI jobs
• log-step: Log the start of a bisection step and retrieve next commit to test. Appends step details to the bisection.log and prints information about the soon-to-be-tested commit to the CI console. If bisection is complete, outputs completion status instead of next commit
• record: Record the CI test result for a commit and update bisection boundaries. Updates the JSON state object with new boundaries and next action
• show-restart: Display and log restart instructions for the current bisection step. Called before running a test so users know how to restart if the job fails as these bisections can be long running jobs
• log-job: Log the execution details of a CI test job to the CI console for easier debugging.
• final-report: Generate comprehensive final report when bisection completes. The report includes session details, first bad commit, commit diff/stats, test result summary, and statistics

The CI job in question would use the script like so

python3 bisect.py init --repo-path llvm-project f71be4038910e897b0ed78a963e00ac1fdc9b6cc a5c751e3253f09567cef180edee60cc19cc5e366 --test-job clang-stage1-RA

while (bisection is not complete) {
  python3 bisect.py log-step --repo-path llvm-project N

  python3 bisect.py show-restart --repo-path llvm-project N clang-stage1-RA --platform jenkins

  <build CI job in question>

  python3 bisect.py log-job --repo-path llvm-project clang-stage1 <(SUCCESS|FAIL)> <DURATION> --job-url https://ci.swift.org/job/clang-stage1-RA/ --build-number <NUM>

  python3 bisect.py record --repo-path llvm-project <COMMIT> <(SUCCESS|FAIL)>
}


python3 bisect.py final-report --repo-path llvm-project

Throughout this process the json state file is updated and used to continue the bisection. Shown to work here:
https://ci.swift.org/view/xInfrastructure/job/wip-run-bisect/

[justice-adams-apple]

cc @azharudd