feat: support vim.g.oil configuration + remove release-please (#17)

* feat: support vim.g.oil declarative configuration

Problem: oil.nvim requires an imperative require("oil").setup(opts)
call to initialize. The Neovim ecosystem is moving toward vim.g.plugin
as a declarative config source that works without explicit setup calls.

Solution: fall back to vim.g.oil in config.setup() when no opts are
passed, and add plugin/oil.lua to auto-initialize when vim.g.oil is
set. Explicit setup(opts) calls still take precedence. Update docs
and add tests for the new resolution order.

Closes: barrettruth/oil.nvim#1

* build: remove release-please pipeline

Problem: the release-please action creates automated releases that
are not needed for this fork's workflow.

Solution: remove the release job from tests.yml and the
release-please branch exclusion from the review request workflow.

* fix(doc): improve readme phrasing

* doc: minor phrasing "improvements"

* ci: add luarocks release on tag push

Problem: there is no automated way to publish oil.nvim to luarocks
when a new version is tagged.

Solution: add a luarocks workflow that triggers on v* tag pushes,
runs the test suite via workflow_call, then publishes via
luarocks-tag-release. Add workflow_call trigger to tests.yml so it
can be reused.

.github/workflows/luarocks.yaml

@@ -0,0 +1,21 @@
+name: luarocks
+
+on:
+  push:
+    tags:
+      - 'v*'
+
+jobs:
+  quality:
+    uses: ./.github/workflows/tests.yml
+
+  publish:
+    needs: quality
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: nvim-neorocks/luarocks-tag-release@v7
+        env:
+          LUAROCKS_API_KEY: ${{ secrets.LUAROCKS_API_KEY }}