feat(pokemon): debounce async validator and reset validating state in finalize

[OrlPep]

Context

The register form’s async Pokémon validator currently issues a network request on each keystroke and toggles the validating spinner accordingly.

Motivation / Problem Statement

Rapid typing triggers multiple unnecessary API calls, keeps the validating spinner active and causes visible flicker as validation rapidly starts/stops. Debouncing prevents redundant requests and avoids unnecessary validation cycles and spinner flicker during continuous typing.

Solution Overview

• Add a 500 ms debounce using timer + switchMap so the request is sent only after typing pauses.
• Move the isPokemonValidating reset into finalize so it runs after both success and error paths (single, consistent state flip).
• Set pokemonId = -1 when the input is empty to reflect the absence of a selected Pokémon and avoid superfluous requests.
• Keep pokemonName updates unchanged aside from the debounce flow.
• Keep the replacement strategy on error:
  catchError(() => of({ pokemonName: true })), ensuring the validator always returns a value (either null or an error object) even when the request fails.

Scope of Change

File changed: src/app/core/validators/pokemon.validator.ts only.
No changes to component templates, routes, or backend APIs.

User-Visible Behavior

1. A validation request is sent only after 500 ms without typing.
2. The validating flag (isPokemonValidating) is set once per validation attempt and reset after completion, no rapid on/off toggles during typing.
3. The spinner no longer flickers during continuous input.
4. Empty input does not trigger a request and clears the stored Pokémon ID (pokemonId = -1).

Testing Instructions

Run: npm i && npm start

1. Open the register page and focus the Pokémon field.
2. Type quickly (e.g., pika…), then pause:
   • Before (reference GIF): multiple requests while typing; spinner toggles rapidly.
   • After: a single request is sent ~500 ms after typing stops; spinner remains steady during the typing phase and turns off after the request completes.
3. Clear the field:
   • No request is made.
   • isPokemonValidating is false.
   • pokemonId becomes -1.
4. Enter a valid Pokémon name → no validation error.

Performance / UI State Notes

• Fewer network requests during continuous typing.
• Fewer spinner state transitions during input (eliminates flicker caused by rapid validation cycles).

Related Links / Issues

N/A

Before / After GIFs

Before

• Multiple API requests sent during rapid typing.
• Spinner toggles on/off multiple times causing visible flicker.

After

• Single API request sent after 500 ms pause.
• Spinner stays steady during typing and stops cleanly after validation completes.

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Checklist

• Lint passes (npm run lint)
• Build passes (npm run build)
• No public API or routing changes
• Attach two short GIFs (before/after) showing request timing and spinner behavior

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[OrlPep]

Removed the extra .toLowerCase() call here because the value was already being normalized earlier in validate().