Implements #5261: Simple rotating per-round save file system.

[Sleet01]

This patch adds user-configurable per-round rotating save files, based on the system used by MekHQ, to MegaMek.

These saves are separate from the other autosaves and default to 3, so the last 3 rounds of the most recent game will be saved. Critically, these save files will not be overwritten by starting MegaMek; a game must actually be entered and the start of a new round must occur for this save system to be triggered.

File name format is "Round-<current round#>-autosave_.sav.gz", e.g. Round-3-autosave_2024-04-13_03-37-08.sav.gz. Note that this means only 3 rotating save files total will be saved, not 3 per separate game. If we want that functionality, more work is required.

Testing:

• Ran small game over several rounds, confirming file rotation works and files can be loaded and resumed.
• Ran all 3 projects' unit tests.

Close #5261

[Sleet01]

Based on comments from the QA team, I would like to strongly advocate for including this functionality in the .19 release in order to facilitate better testing results.

[Sleet01]

Files from a short Princess v Princess game:

[Sleet01]

New Game Option location:

[HoneySkull]

reviewed the code - looks good.

[HoneySkull]

Can you test this with:

1. Maximum Rotating Saves set to 0.
2. Change the configured save path in the properties set to something other than the default.
3. Using the default megamek config file (as if from a new fresh install)

[Thom293]

I can test this in about 10 hours if no one gets to it first.

[Sleet01]

I can test this in about 10 hours if no one gets to it first.

I have some errands to run this morning, but hopefully will knock the extra testing out after lunch.

[Sleet01]

Can you test this with:

1. Maximum Rotating Saves set to 0.
2. Change the configured save path in the properties set to something other than the default.
3. Using the default megamek config file (as if from a new fresh install)

@HoneySkull @Thom293 Tested and confirmed:

1. Setting Max to 0 prevents new rotating saves (and prevents deleting old rotating saves).
2. Changing the configured save path in properties causes saves, including rotating saves, to appear in the new dir.
3. Default config file sets Maximum Rotating Saves to 3.

Given that, I'm going to pull this.