feat: improvements in package caching

[a-gave]

This adds some squid directives to consider fresh longer kernel modules of already compiled releases, to prevent revalidation against the origin server which consumes time.

An automatic mechanism to refresh the below squid directive should be included (e.g., 24h after the first appearance on https://downloads.openwrt.org/.versions.json)

refresh_pattern ^http://downloads.openwrt.org/releases/.*(23.05.[6-99]|24.10.[1-99]|25.*|SNAPSHOT)/targets/.* 0 100% 0 refresh-ims

This adds also a fallback to no_proxy (https) in case STDERR contains “package index are corrupt” to rule out cache problems and to allow packages to be considered fresh longer and thus not revalidated against the origin server

[codecov]

Codecov Report

Attention: Patch coverage is 52.38095% with 10 lines in your changes missing coverage. Please review.

Project coverage is 90.29%. Comparing base (5e65dec) to head (dc53a56).
Report is 225 commits behind head on main.

Files with missing lines	Patch %	Lines
asu/build.py	25.00%	6 Missing ⚠️
asu/util.py	69.23%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1274      +/-   ##
==========================================
+ Coverage   80.75%   90.29%   +9.53%     
==========================================
  Files          15       13       -2     
  Lines         977     1205     +228     
==========================================
+ Hits          789     1088     +299     
+ Misses        188      117      -71     

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[aparcar]

I recon you're really limited on bandwidth? Or what is the motivation to avoid the extra checks?