feat: Fix keychain issues and add fs fallback (#10)

- Add missing features for `keyring` to make it actually work instead of
being a no-op (grr)
- Allow option for storing token in a file as a fallback for keychain
issues (disabled by default)
- Add ability to get debug logging

---------

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>
Co-authored-by: Jay Gowdy <130084966+jgowdy-godaddy@users.noreply.github.com>

Author: 3 people

.github/workflows/ci.yml

@@ -23,19 +23,19 @@ jobs:
         run: cargo fmt --all --check
 
       - name: Check
-        run: cargo check --all-targets
+        run: cargo check --all-targets && cargo check --all-targets --features pkce-auth
 
       - name: Clippy
-        run: cargo clippy --all-targets -- -D warnings
+        run: cargo clippy --all-targets -- -D warnings && cargo clippy --all-targets --features pkce-auth -- -D warnings
 
       - name: Test
-        run: cargo test --all-targets
+        run: cargo test --all-targets && cargo test --all-targets --features pkce-auth
 
       - name: Docs
-        run: RUSTDOCFLAGS='-D warnings' cargo doc --no-deps
+        run: RUSTDOCFLAGS='-D warnings' cargo doc --no-deps && RUSTDOCFLAGS='-D warnings' cargo doc --no-deps --features pkce-auth
 
       - name: Doc Tests
-        run: cargo test --doc
+        run: cargo test --doc && cargo test --doc --features pkce-auth
 
       - name: Publish dry run
         run: cargo publish --dry-run