feat: upgrade to Angular 21

[LuisWolf-Snapaddy]

Addresses:

• Please update dependencies for Angular 21 #2072

What kind of change does this PR introduce? (check one with "x")

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Other... Please describe:
  • Upgrade to Angular v21 using ng update
    • Automatically ran control-flow migration
    • Used else block instead of duplicate negated if block
    • Fixed tracking so hopefully more unique identifiers are used
  • Upgrade to some other libraries
    • Especially Prettier to correctly format control-flow

What is the current behavior? (You can also link to an open issue here)

• Not compatible with Angular 21

What is the new behavior?

• Compatible with Angular v21

Does this PR introduce a breaking change? (check one with "x")

• Yes
• No

If this PR contains a breaking change, please describe the impact and migration path for existing applications: ...

Other information:

• I started the demo application and everything seems to work fine
• I was not able to test the library in our own application, since I didn't publish it / symlinked it into the node_modules

---

Note

Upgrade to Angular v21 and template migration

• Bumps Angular framework/tooling to 21.1.x and updates related deps (RxJS, Zone.js, AJV, d3 types, ESLint plugins, ng-packagr, Karma, TypeScript 5.9, Prettier 3)
• Migrates templates from *ngIf/*ngFor to Angular control-flow (@if, @for) across chart components (area, bar, line, bubble, heat map, gauge, number-card, axes, legends, common)
• Removes old trackBy implementations and associated imports; leverages @for tracking expressions
• Minor refactors/constructor formatting and gradient/tooltip rendering adjustments to align with new template syntax
• No API changes noted; goal is Angular 21 compatibility

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[daiscog]

@marjan-georgiev @steveblue are you able to help get this merged please?