Add support to specify a purchase date in config

[DerpingtonDerp]

This PR adds support to specify a purchase date in configs.app.ini.

Some games check using GetEarliestPurchaseUnixTime when the game was purchased to provide preorder bonus items.
The old logic will be used by default if no purchase_date has been specific in configs.app.ini.

[alex47exe]

May I ask first why it defaults to 4 days before launch? Can you make that configurable as well, or even add a third option like defaulting to a fixed date?

[Copilot]

Pull Request Overview

This PR adds support for specifying a purchase date through the configuration file, enabling certain games to properly calculate preorder bonuses based on custom purchase timestamps.

• Added a new "purchase_date" configuration key in the ini file.
• Updated GetEarliestPurchaseUnixTime in steam_apps.cpp to use the parsed purchase date.
• Implemented parse_purchase_date in settings_parser.cpp and added getter/setter functions in Settings.

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

File	Description
post_build/steam_settings.EXAMPLE/configs.app.EXAMPLE.ini	Added a new purchase_date config entry with descriptive comments.
dll/steam_apps.cpp	Modified GetEarliestPurchaseUnixTime to use the new purchase date from settings.
dll/settings_parser.cpp	Introduced parse_purchase_date to parse and fallback on the purchase_date value.
dll/settings.cpp & dll/dll/settings.h	Added getter and setter for purchase_date in the Settings class.

Comments suppressed due to low confidence (1)

post_build/steam_settings.EXAMPLE/configs.app.EXAMPLE.ini:17

• [nitpick] Clarify if the empty default value is intended to trigger a fallback behavior and consider documenting the expected format and fallback logic more explicitly.

# default=

[Copilot]

Consider adding a log warning here when parsing fails, to help with diagnosing misconfigured purchase dates.

[DerpingtonDerp]

4 days before launch was the default value that was returned before adding this change.
Therefore the 4 days was chosen as a fallback when no specific purchase date has been set.
Important to not it is 4 days before the launch day, meaning if you start the game at 06/30/2025 10:00:00 it will return 06/26/2025 10:00:00 as the earliest purchase date. This is the logic that was always applied by the Goldberg emu for the GetEarliestPurchaseDate.
Adding another option for customizing the time shift from game launch would not be useful at all. Then you could just set the date of purchase itself and will always be the same and not change if you for example start the game at another day.