Pending detection, FX metadata, Pending UI badge. (#374)

* - Add support for `SIMPLEFIN_INCLUDE_PENDING` to control pending behavior via ENV.
- Enhance debug logging for SimpleFin API requests and raw payloads.
- Refine pending flag handling in `SimplefinEntry::Processor` based on provider data and inferred conditions.
- Improve FX metadata processing for transactions with currency mismatches.
- Add new tests for pending detection, FX metadata, and edge cases involving `posted` values.
- Add pending indicator UI to transaction view.

* Document pending transaction detection, storage, and UI behavior for SimpleFIN and Plaid integrations. Add debug flags for troubleshooting.

* Add `pending?` method to `Transaction` model, refactor UI indicator, and centralize SimpleFIN configuration

- Introduced `pending?` method in `Transaction` for unified pending state detection.
- Refactored transaction pending indicator in the UI to use `pending?` method.
- Centralized SimpleFIN configuration in initializer with ENV-backed toggles.
- Updated tests for `pending?` behavior and clarified docs for pending detection logic

* Add SimpleFIN debug and runtime flags to `.env.local.example` and `.env.test.example`

- Introduced `SIMPLEFIN_INCLUDE_PENDING` and `SIMPLEFIN_DEBUG_RAW` flags for controlling pending behavior and debugging.
- Updated example environment files with descriptions for new configuration options.

* Normalize formatting for `SIMPLEFIN_INCLUDE_PENDING` and `SIMPLEFIN_DEBUG_RAW` flags in `.env.local.example` and `.env.test.example`.

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Co-authored-by: Josh Waldrep <joshua.waldrep5+github@gmail.com>

app/models/provider/simplefin.rb

@@ -1,4 +1,9 @@
 class Provider::Simplefin
+  # Pending: some institutions do not return pending transactions even with `pending=1`.
+  # This is provider variability (not a bug). For troubleshooting, you can set
+  # `SIMPLEFIN_INCLUDE_PENDING=1` and/or `SIMPLEFIN_DEBUG_RAW=1` (both default-off).
+  # These are centralized in `Rails.configuration.x.simplefin.*` via
+  # `config/initializers/simplefin.rb`.
   include HTTParty
 
   headers "User-Agent" => "Sure Finance SimpleFin Client"