Update Svelte integration guide for Svelte 5 and runes

[sequba]

Context

The Svelte integration guide was written for Svelte 4 and needs to be updated to reflect Svelte 5's new runes-based reactivity system. The changes modernize the code examples and clarify best practices for using HyperFormula with current Svelte versions.

Changes

• Target Svelte 5 (runes mode): Updated all code examples to use the $state rune for reactive variables instead of plain let declarations
• Event handler syntax: Changed from on:click to onclick to match Svelte 5 conventions
• Type annotations: Added TypeScript support with proper imports (import type) and inline type annotations using $state<Type>()
• SSR guidance: Clarified the SvelteKit SSR section with better explanation of why onMount is necessary and corrected the async cleanup pattern (separate onDestroy instead of returning cleanup from async onMount)
• Reactivity explanations: Added detailed notes about when to use $state (for values that drive UI updates) vs. plain const (for references that never change, like the HyperFormula instance)
• Best practices: Documented that table cell expressions don't need reactivity since they read static data, and explained how to handle mutations if needed

How did you test your changes?

Documentation review — verified that all code examples follow Svelte 5 patterns and are syntactically correct. The changes are purely documentation updates with no runtime code modifications.

Types of changes

• Change to the documentation

Checklist:

• I have reviewed the guidelines about Contributing to HyperFormula and I confirm that my code follows the code style of this project.
• My changes require a documentation update.

https://claude.ai/code/session_0123ZjQT79obK9A6DXCwaKUW

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.18%. Comparing base (d6a316c) to head (7c77f50).

Additional details and impacted files

@@                             Coverage Diff                              @@
##           feature/hf-122-framework-integration-guides    #1659   +/-   ##
============================================================================
  Coverage                                        97.18%   97.18%           
============================================================================
  Files                                              174      174           
  Lines                                            15086    15086           
  Branches                                          3223     3223           
============================================================================
  Hits                                             14662    14662           
  Misses                                             424      424           

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[github-actions]

Performance comparison of head (7c77f50) vs base (d6a316c)

                                     testName |   base |   head | change
------------------------------------------------------------------------
                                      Sheet A | 487.59 | 487.07 | -0.11%
                                      Sheet B | 157.14 | 155.78 | -0.87%
                                      Sheet T | 139.25 | 140.09 | +0.60%
                                Column ranges |  471.1 | 473.29 | +0.46%
Sheet A:  change value, add/remove row/column |  15.54 |  15.18 | -2.32%
 Sheet B: change value, add/remove row/column | 132.81 | 131.66 | -0.87%
                   Column ranges - add column | 142.34 | 146.85 | +3.17%
                Column ranges - without batch |  433.5 | 443.18 | +2.23%
                        Column ranges - batch | 112.13 | 111.68 | -0.40%