Improve read performance with caching and memoization (#4572)

* Improve read performance with caching and memoization

- Memoize `Crop#all_companions` and `Member#unread_count` in models
- Implement instance-level memoization in `CropsHelper#crop_or_parent`
- Add Rails caching for expensive aggregate queries in `Charts::CropsController`
- Add fragment caching for high-impact sections on the crop show page

Co-authored-by: CloCkWeRX <365751+CloCkWeRX@users.noreply.github.com>

* Fix header spec failure due to memoized unread_count

- Reset `@unread_count` in `spec/views/layouts/_header_spec.rb` to ensure the updated notification count is rendered correctly.

Co-authored-by: CloCkWeRX <365751+CloCkWeRX@users.noreply.github.com>

---------

Co-authored-by: google-labs-jules[bot] <161369871+google-labs-jules[bot]@users.noreply.github.com>

app/models/crop.rb

@@ -165,9 +165,11 @@ class Crop < ApplicationRecord
   end
 
   def all_companions
-    return companions unless parent
-
-    (companions + parent.all_companions).uniq
+    @all_companions ||= if parent
+                          (companions + parent.all_companions).uniq
+                        else
+                          companions
+                        end
   end
 
   before_destroy :destroy_reverse_companionships

app/views/crops/show.html.haml

@@ -36,10 +36,11 @@
       = cute_icon
       = render 'predictions', crop: @crop
     - if @crop.all_companions.any?
-      %section.companions
-        %h2 Companions
-        - @crop.all_companions.each do |companion|
-          = render 'crops/tiny', crop: companion
+      - cache [@crop, 'companions'] do
+        %section.companions
+          %h2 Companions
+          - @crop.all_companions.each do |companion|
+            = render 'crops/tiny', crop: companion
 
     - if crop_or_parent(@crop, :en_youtube_url).present?
       %section.youtube