chore: abstract pg test logic and double runner sizes (#21091)

This PR does two things, both in service of helping to (hopefully!)
speed up CI:

1. abstracts the parallelism logic into a common action and has all
PG-related jobs use it
2. doubles runner sizes from [8->16 CPUs & 32->64GiB
RAM](https://depot.dev/docs/github-actions/runner-types)* and
concomitantly increases parallelism

I only focused on the PG-related jobs since they are generally slowest &
most RAM-intensive.

[<img width="2011" height="460" alt="image"
src="https://github.com/user-attachments/assets/c38ec3fc-dd93-4753-8df3-f22dfe54a3f7"
/>](https://app.datadoghq.com/ci/pipelines/health?query=%40git.repository.id_v2%3Agithub.com%2Fcoder%2Fcoder%20-%40git.is_default_branch%3Atrue&fromUser=true&group=ci-cost&sort=-billableTime&sp=%5B%7B%22p%22%3A%7B%22fingerprint%22%3A%22pVB6pq7htXrn%22%2C%22env%22%3A%22none%22%7D%2C%22i%22%3A%22ci-health-pipeline-panel%22%7D%5D&start=1762245172958&end=1764837172958&paused=false)

_* `test-go-race-pg` doubles from 16->32 CPUs & 64->128GiB RAM and
likewise for the Windows runners; MacOS runners have [only one
size](https://depot.dev/docs/github-actions/runner-types#macos-runners)_

_**NOTE:** don't use the speed of the PG-related jobs in this PR's CI
run as indicative. Tests run outside `main` may use cache, so the speed
may seem artificially low._

---------

Signed-off-by: Danny Kopping <danny@coder.com>

.github/actions/test-go-pg/action.yaml

@@ -0,0 +1,79 @@
+name: "Test Go with PostgreSQL"
+description: "Run Go tests with PostgreSQL database"
+
+inputs:
+  postgres-version:
+    description: "PostgreSQL version to use"
+    required: false
+    default: "13"
+  test-parallelism-packages:
+    description: "Number of packages to test in parallel (-p flag)"
+    required: false
+    default: "8"
+  test-parallelism-tests:
+    description: "Number of tests to run in parallel within each package (-parallel flag)"
+    required: false
+    default: "8"
+  race-detection:
+    description: "Enable race detection"
+    required: false
+    default: "false"
+  test-count:
+    description: "Number of times to run each test (empty for cached results)"
+    required: false
+    default: ""
+  test-packages:
+    description: "Packages to test (default: ./...)"
+    required: false
+    default: "./..."
+  embedded-pg-path:
+    description: "Path for embedded postgres data (Windows/macOS only)"
+    required: false
+    default: ""
+  embedded-pg-cache:
+    description: "Path for embedded postgres cache (Windows/macOS only)"
+    required: false
+    default: ""
+
+runs:
+  using: "composite"
+  steps:
+    - name: Start PostgreSQL Docker container (Linux)
+      if: runner.os == 'Linux'
+      shell: bash
+      env:
+        POSTGRES_VERSION: ${{ inputs.postgres-version }}
+      run: make test-postgres-docker
+
+    - name: Setup Embedded Postgres (Windows/macOS)
+      if: runner.os != 'Linux'
+      shell: bash
+      env:
+        POSTGRES_VERSION: ${{ inputs.postgres-version }}
+        EMBEDDED_PG_PATH: ${{ inputs.embedded-pg-path }}
+        EMBEDDED_PG_CACHE_DIR: ${{ inputs.embedded-pg-cache }}
+      run: |
+        go run scripts/embedded-pg/main.go -path "${EMBEDDED_PG_PATH}" -cache "${EMBEDDED_PG_CACHE_DIR}"
+
+    - name: Run tests
+      shell: bash
+      env:
+        TEST_NUM_PARALLEL_PACKAGES: ${{ inputs.test-parallelism-packages }}
+        TEST_NUM_PARALLEL_TESTS: ${{ inputs.test-parallelism-tests }}
+        TEST_COUNT: ${{ inputs.test-count }}
+        TEST_PACKAGES: ${{ inputs.test-packages }}
+        RACE_DETECTION: ${{ inputs.race-detection }}
+        TS_DEBUG_DISCO: "true"
+        LC_CTYPE: "en_US.UTF-8"
+        LC_ALL: "en_US.UTF-8"
+      run: |
+        set -euo pipefail
+
+        if [[ ${RACE_DETECTION} == true ]]; then
+          gotestsum --junitfile="gotests.xml" --packages="${TEST_PACKAGES}" -- \
+            -race \
+            -parallel "${TEST_NUM_PARALLEL_TESTS}" \
+            -p "${TEST_NUM_PARALLEL_PACKAGES}"
+        else
+          make test
+        fi