SettingsProtectionHelper: support always-hidden controls

[imnasnainaec]

Summary

• Add SetSettingsProtection(Control, bool, bool keepHidden) and SetSettingsProtection(ToolStripItem, bool, bool keepHidden) overloads so a control or ToolStripItem can be marked always-hidden, staying hidden even while Ctrl+Shift reveals the other protected components. The original 2-parameter overloads are preserved for WinForms designer extender-property discovery and binary compatibility.
• Track always-hidden components in a separate _alwaysHiddenComponents set, which UpdateDisplay() hides unconditionally after the normal pass. GetSettingsProtection reports true for them too.
• Apply always-hidden registration immediately at run time instead of leaving the component visible until the next (~100 ms) timer tick. Design time is deliberately excluded: the extender property setter runs there as well, where the timer is off and the component must stay visible on the design surface.
• Apply the normal visibility rule immediately when a component leaves always-hidden, so the two directions are symmetric. The !NormallyHidden || Ctrl+Shift rule moved into a property shared with UpdateDisplay(), which had been recomputing it once per component.
• Rework Dispose(bool) into the standard form used elsewhere in the repo — the missing-Dispose debug warning, an early return that makes it idempotent, managed cleanup only when disposing, and _isDisposed set after base.Dispose(disposing). That ordering matters: Component.Dispose removes itself from its container, which reads the Site property, and this class overrides Site to throw once disposed. The explicit _checkForCtrlKeyTimer.Dispose() is gone, since the timer is owned by the components container that disposes it.
• Give both new overloads full XML documentation (summary plus a tag for every parameter).
• Add SettingsProtectionHelperTests — 11 tests covering normal vs. always-hidden visibility, both transition directions and their immediacy, unprotecting, GetSettingsProtection, and disposing while still sited in a container.
• Add CHANGELOG entries under Added and Fixed.

Scope note on #1134

keepHidden is a "never show this" primitive: an always-hidden component is not revealed by Ctrl+Shift, and it is not revealed by entering the settings password either — nothing records that the password was entered, and UpdateDisplay() re-hides these components on every tick.

#1134 asks for components that remain hidden unless the password is entered. A client can build that on top of this: mark the components keepHidden: true, then re-register them with keepHidden: false after a successful challenge. This PR does not add that behavior to the library itself.

Fixes #1134

Devin review: https://app.devin.ai/review/sillsdev/libpalaso/pull/1522

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This change is

[github-actions]

Palaso Tests

     4 files  ± 0       4 suites  ±0   10m 27s ⏱️ ±0s
 5 119 tests +11   4 885 ✅ +10  234 💤 +1  0 ❌ ±0 
16 669 runs  +33  15 948 ✅ +32  721 💤 +1  0 ❌ ±0 

Results for commit 4fdbee4. ± Comparison against base commit e65a140.

This pull request skips 1 test.

SIL.Tests.IO.FileLocationUtilitiesTests ‑ LocateInProgramFiles_SendValidProgramDeepSearch_ReturnsProgramPath

♻️ This comment has been updated with latest results.

[papeh]

@papeh reviewed 1 file and made 1 comment.
Reviewable status: 1 of 4 files reviewed, 2 unresolved discussions (waiting on imnasnainaec).

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SIL.Windows.Forms/SettingProtection/SettingsProtectionHelper.cs line 77 at r1 (raw file):

			foreach (var component in _componentsUnderSettingsProtection)
			{
				bool visible = !SettingsProtectionSingleton.Settings.NormallyHidden || ((Control.ModifierKeys & keys) == keys);

nice improvement!

[imnasnainaec]

@imnasnainaec reviewed all commit messages and made 1 comment.
Reviewable status: 0 of 4 files reviewed, 2 unresolved discussions (waiting on papeh).

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SIL.Windows.Forms/SettingProtection/SettingsProtectionHelper.cs line 77 at r1 (raw file):

Previously, papeh wrote…

nice improvement!

Thanks!