chore: scaffold workspace with nextest and docker compose

Workspace with 6 crates: wfe-core, wfe-sqlite, wfe-postgres,
wfe-opensearch, wfe-valkey, and wfe (umbrella). Nextest profiles
for default, integration, and CI. Docker compose for PostgreSQL,
Valkey, and OpenSearch integration tests.

.config/nextest.toml

@@ -0,0 +1,40 @@
+[store]
+dir = "target/nextest"
+
+[profile.default]
+test-threads = "num-cpus"
+status-level = "pass"
+final-status-level = "flaky"
+failure-output = "immediate-final"
+success-output = "never"
+fail-fast = true
+slow-timeout = { period = "30s", terminate-after = 2 }
+
+[profile.default.junit]
+path = "target/nextest/default/junit.xml"
+
+[profile.integration]
+test-threads = 4
+fail-fast = false
+slow-timeout = { period = "120s", terminate-after = 2 }
+failure-output = "immediate-final"
+retries = 1
+
+[profile.integration.junit]
+path = "target/nextest/integration/junit.xml"
+
+[profile.ci]
+fail-fast = false
+test-threads = "num-cpus"
+failure-output = "immediate-final"
+success-output = "final"
+slow-timeout = { period = "60s", terminate-after = 3 }
+retries = 2
+
+[profile.ci.junit]
+path = "target/nextest/ci/junit.xml"
+
+# Postgres tests must run serially (shared database state)
+[[profile.default.overrides]]
+filter = "package(wfe-postgres)"
+threads-required = "num-cpus"