Upgrade to Rails 8 defaults and clean up

[larouxn]

Description

Proposing we upgrade from Rails 7.2 to Rails 8 defaults. We're already using two of the three new Rails 8.0 defaults. The only one we're not currently using is action_dispatch.strict_freshness = true but that's really just RFC 7232 spec compliance and as such unlikely to cause any issues. All in all this is more of no-op cleanup than any serious upgrade.

rubygems.org/config/application.rb

Lines 32 to 40 in 6b85477

	###
	# TODO: This is a 8.0 framework default, but load order requires it to be here to avoid deprecation warnings.
	#
	# Specifies whether `to_time` methods preserve the UTC offset of their receivers or preserves the timezone.
	# If set to `:zone`, `to_time` methods will use the timezone of their receivers.
	# If set to `:offset`, `to_time` methods will use the UTC offset.
	# If `false`, `to_time` methods will convert to the local system UTC offset instead.
	#++
	Rails.application.config.active_support.to_time_preserves_timezone = :zone

rubygems.org/config/initializers/new_framework_defaults_8_0.rb

Line 22 in 6b85477

Regexp.timeout = 1

Inspired by #6275

How?

1. Bump defaults from 7.2 to 8.0
2. Remove active_support.to_time_preserves_timezone config as such is now default
3. Remove new_framework_defaults_8_0.rb including its Regexp.timeout config as such is now default

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 38.02%. Comparing base (dd5c605) to head (9a9e568).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6277      +/-   ##
==========================================
- Coverage   38.65%   38.02%   -0.63%     
==========================================
  Files         487      487              
  Lines       10728    10787      +59     
==========================================
- Hits         4147     4102      -45     
- Misses       6581     6685     +104     

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