Avoid N+1 calls for image_path when rendering commits

What does this MR do?

When rendering projects/commits/commit partial, it calls some helper methods like sprite_icon and clipboard_button.

These methods call sprite_icon_path internally which is not that slow (averaging around 6ms per call on my local machine). But when called multiple times (e.g. rendering 100 commits), it adds up. Memoizing the method helps in reducing the number of calls.

Some benchmark numbers for Projects::MergeRequestsController#commits (average of 5 requests, with RAILS_PROFILE env var set to true:

• BEFORE: 1.051528
• AFTER: 0.684848

This shows around 35% improvement.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• [-] Label as security and @ mention @gitlab-com/gl-security/appsec
• [-] The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• [-] Security reports checked/validated by a reviewer from the AppSec team

#209912