Ensure meal is only saved once

[MikePlante1]

• Disables the Save and continue button after it's pressed until the AddCarbs module is reopened.
• Renames saved flag to noteSaved for clarity.
• Addresses Duplicated carb entries #175

[bjornoleh]

This looks great, and seems to do what it says.

There is no noticeable impact on the workflow for normal carb entries, and the mealSaved flag should be set to true as soon as the "Save and continue" button is pressed, and should block a second entry if the app is hanging.

I also tested changing @State var mealSaved from false to true to confirm that this state would disable the "Save and continue" button. This disabled the button as expected.

LGTM!

[aug0211]

• Multiple days of testing in vitro and in vivo, 0 issues encountered
• Button grays out as expected immediately on tap
• Attempted to recreate instigating issue a number of times in vivo with a looping pump (and CGM) connected by entering carbs during loop cycle
• 0 instances resulted in duplicate carbs, despite my best efforts to break it
• 0 other issues observed over the course of multiple meal entries (both in vitro and in vivo)

[aug0211]

See comments, tested in vitro and in vivo with 0 issue and was unable to reproduce initial issue (which is a good thing in this case).

[dnzxy]

Basing approval on code review only. LGTM. Precise, intentional changes. We have two test accounts by experienced testers.

[dnzxy]

Merging with 2 testers (in-vitro and in-vivo) and 3 approvals.

[MikePlante1]

From the code, I'm pretty confident the button won't be able to be pressed twice, but I've still been spamming the "save" button every time I log meals the past few days and haven't had it trigger twice, even when purposely entering during a loop cycle.