Introduce .rspec config and drop RUBYOPT=-w from CI workflows

Mirror the `.rspec` from rsim/oracle-enhanced:

    --force-color
    --backtrace
    --require spec_helper
    --warnings

The `--warnings` flag replaces the per-workflow `RUBYOPT=-w` prefix on
`bundle exec rspec`, so the same warning surface is now driven from a
single project-level file rather than seven workflow scripts plus one
workflow-level env block in devcontainer.yml. `--force-color` and
`--backtrace` make CI logs (and local runs) more debuggable;
`--require spec_helper` lets individual specs skip the require eventually.

No spec changes; spec/plsql/procedure_spec.rb stays green
(195 examples, 0 failures, 1 pre-existing pending) and no new warnings
are emitted with `--warnings` on.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: yahonda

.github/workflows/devcontainer.yml

@@ -5,9 +5,6 @@ on:
     - cron: "0 6 1 * *"  # 1st of every month at 6:00 AM UTC
   workflow_dispatch:
 
-env:
-  RUBYOPT: "-w"
-
 jobs:
   test:
     runs-on: ubuntu-latest

.github/workflows/jruby_head.yml

@@ -72,4 +72,4 @@ jobs:
         bundle install --jobs 4 --retry 3
     - name: Run RSpec
       run: |
-        RUBYOPT=-w bundle exec rspec
+        bundle exec rspec

.github/workflows/ruby_head.yml

@@ -78,4 +78,4 @@ jobs:
         bundle install --jobs 4 --retry 3
     - name: Run RSpec
       run: |
-        RUBYOPT=-w bundle exec rspec
+        bundle exec rspec

.github/workflows/test.yml

@@ -90,4 +90,4 @@ jobs:
         bundle install --jobs 4 --retry 3
     - name: Run RSpec
       run: |
-        RUBYOPT=-w bundle exec rspec
+        bundle exec rspec

.github/workflows/test_11g.yml

@@ -96,4 +96,4 @@ jobs:
         bundle install --jobs 4 --retry 3
     - name: Run RSpec
       run: |
-        RUBYOPT=-w bundle exec rspec
+        bundle exec rspec

.github/workflows/test_11g_ojdbc11.yml

@@ -91,4 +91,4 @@ jobs:
         bundle install --jobs 4 --retry 3
     - name: Run RSpec
       run: |
-        RUBYOPT=-w bundle exec rspec
+        bundle exec rspec

.github/workflows/test_gemfiles.yml

@@ -104,4 +104,4 @@ jobs:
         bundle install --jobs 4 --retry 3
     - name: Run RSpec
       run: |
-        RUBYOPT=-w bundle exec rspec
+        bundle exec rspec

.github/workflows/truffleruby.yml

@@ -79,4 +79,4 @@ jobs:
         bundle install --jobs 4 --retry 3
     - name: Run RSpec
       run: |
-        RUBYOPT=-w bundle exec rspec
+        bundle exec rspec

.rspec

@@ -0,0 +1,4 @@
+--force-color
+--backtrace
+--require spec_helper
+--warnings