[ty] ecosystem-analyzer workflow (#18719)

## Summary

Adds a new ecosystem-analyzer workflow with a similar purpose to the
mypy-primer workflow. It creates a richer ecosystem diff report using
[ecosystem-analyzer](https://github.com/astral-sh/ecosystem-analyzer/)
([example
report](https://shark.fish/diff-attr-subscript-narrowing.html)). This is
still experimental and also quite a bit slower than mypy_primer, so I
chose to make this opt-in for now via a `ecosystem-analyzer` label. This
would give us a way to play with this while still evaluating if we
should further invest in this or not.

Advantages over the mypy_primer diff output:
- Interactive filtering of diagnostics
- Statistics overview which breaks down added/removed/changed
diagnostics across lint rules
- Has the concept of "changed" diagnostics, which makes it easier to
review changes where diagnostic messages have changed (along with other
changes).
- Compute diff based on old and new project-lists (`good.txt`). This
allows us to diff changes to the project list itself. This has caused
confusion in the past where we tried to add new projects to `good.txt`,
but then ran the `main`-branch version of ty on that new list (where the
bug was not yet fixed)

Disadvantages:
- The report currently needs to be downloaded from the workflow run, as
I don't know if we have a way of deploying HTML files like this
temporarily to some hosted infrastructure.

.github/workflows/ty-ecosystem-analyzer.yaml

@@ -0,0 +1,94 @@
+name: ty ecosystem-analyzer
+
+permissions: {}
+
+on:
+  pull_request:
+    types: [labeled]
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref_name }}-${{ github.event.pull_request.number || github.sha }}
+  cancel-in-progress: true
+
+env:
+  CARGO_INCREMENTAL: 0
+  CARGO_NET_RETRY: 10
+  CARGO_TERM_COLOR: always
+  RUSTUP_MAX_RETRIES: 10
+  RUST_BACKTRACE: 1
+  REF_NAME: ${{ github.ref_name }}
+
+jobs:
+  ty-ecosystem-analyzer:
+    name: Compute diagnostic diff
+    runs-on: depot-ubuntu-22.04-32
+    timeout-minutes: 20
+    if: contains(github.event.label.name, 'ecosystem-analyzer')
+    steps:
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+        with:
+          path: ruff
+          fetch-depth: 0
+          persist-credentials: false
+
+      - name: Install the latest version of uv
+        uses: astral-sh/setup-uv@f0ec1fc3b38f5e7cd731bb6ce540c5af426746bb # v6.1.0
+
+      - uses: Swatinem/rust-cache@9d47c6ad4b02e050fd481d890b2ea34778fd09d6 # v2.7.8
+        with:
+          workspaces: "ruff"
+
+      - name: Install Rust toolchain
+        run: rustup show
+
+      - name: Compute diagnostic diff
+        shell: bash
+        run: |
+          cd ruff
+
+          echo "Enabling configuration overloads (see .github/mypy-primer-ty.toml)"
+          mkdir -p ~/.config/ty
+          cp .github/mypy-primer-ty.toml ~/.config/ty/ty.toml
+
+          echo "new commit"
+          git checkout -b new_commit "$GITHUB_SHA"
+          git rev-list --format=%s --max-count=1 new_commit
+          cp crates/ty_python_semantic/resources/primer/good.txt projects_new.txt
+
+          echo "old commit (merge base)"
+          MERGE_BASE="$(git merge-base "$GITHUB_SHA" "origin/$GITHUB_BASE_REF")"
+          git checkout -b old_commit "$MERGE_BASE"
+          git rev-list --format=%s --max-count=1 old_commit
+          cp crates/ty_python_semantic/resources/primer/good.txt projects_old.txt
+
+          cd ..
+
+          uv tool install "git+https://github.com/astral-sh/ecosystem-analyzer@9c34dc514ee9aef6735db1dfebb80f63acbc3440"
+
+          ecosystem-analyzer \
+            --repository ruff \
+            analyze \
+            --projects ruff/projects_old.txt \
+            --commit old_commit \
+            --output diagnostics_old.json
+
+          ecosystem-analyzer \
+            --repository ruff \
+            analyze \
+            --projects ruff/projects_new.txt \
+            --commit new_commit \
+            --output diagnostics_new.json
+
+          ecosystem-analyzer \
+            generate-diff \
+            diagnostics_old.json \
+            diagnostics_new.json \
+            --old-name "main (merge base)" \
+            --new-name "$REF_NAME" \
+            --output-html diff.html
+
+      - name: Upload HTML diff report
+        uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # v4.6.2
+        with:
+          name: diff.html
+          path: diff.html