Cache compiled Stencil templates and move rendering off main thread

[dfsm]

BundleResourceLoader now caches parsed Template objects in an NSCache, eliminating redundant disk I/O and lexer passes on every render cycle.
Template rendering in renderPosts() is moved to a detached task to avoid blocking the main thread during page loads.

[dfsm]

This PR and the HTMLReader PR are related. Both came out of some Time Profiler testing using Instruments.

Before and After for both changes:

Before vs After (recursive sample counts)

Function	Before	After
HTMLSelector initWithString:	18	0 (gone)
SelectorFunctionForString	17	0 (gone)
Lexer.init	present	0 (gone)
Template.init	present	0 (gone)
BundleResourceLoader.loadTemplate	present	0 (gone)

Template re-parsing and selector re-compilation are completely eliminated from the hot path.

[nolanw]

Looks good!

Do you want to bring the cached selectors over to this PR too? I’m good either way. Feel free to merge if not :) also the cached selectors could certainly be a category on HTMSelector/HTMLElement if that’s the nicest way.

[dfsm]

Looks good!

Do you want to bring the cached selectors over to this PR too? I’m good either way. Feel free to merge if not :) also the cached selectors could certainly be a category on HTMSelector/HTMLElement if that’s the nicest way.

Ah yep, no worries. I will bring cached selectors over to this PR so that the issue doesn't keep getting flagged in future instrument runs. i'm trying to automate some testing and instruments stuff

thanks for the quick review.
I'll add another comment to request another review after pushing those changes to this branch

[dfsm]

Hello, I've added the cached selectors now