Manifest cache one key per file doesn't make any sense

[lekoala]

Description

Currently, there is one cache key per file as per

silverstripe-framework/src/Core/Manifest/ClassManifest.php

Line 588 in 2d472f4

$key = preg_replace('/[^a-zA-Z0-9_]/', '_', $basename ?? '') . '_' . md5_file($pathname ?? '');

i don't know if it's the case for others, but in my case, most of the cache ends up in one file, while 2342 get created

this leads to a lot of I/O when using file based cache

there should be a way to have only one key being used. this would allow to load the cache from file only once, not having to make a cache hit for each single file
actually, i believe what is supposed to be lighter (one key per file to only change the files that have been changed) actually leads to a much heavier process when you could simply dump the whole array only once.

Additional context or points of discussion

No response

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