fix: add UnsupportedCapabilityError to handle capabilities custom exception

[matteo-gobbo]

Replace generic Error with UnsupportedCapabilityError when capabilities are not supported, allowing applications to distinguish capability errors from actual failures.

Motivation and Context

It fixes the issue #430

How Has This Been Tested?

Breaking Changes

There are no breaking changes.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional context

Added UnsupportedCapabilityError class in packages/core/src/types/types.ts.
I assigned to it an error code of -32043 following what's been done before, but it should be checked if it's correct.

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Latest commit: 3086e54

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commit: 3086e54

[KKonstantinov]

Hi, thank you for this. The idea if differentiating on various Errors is something we should apply in other places too so users can distinguish them easier.

I've left two comments to be addressed please

[matteo-gobbo]

Hi @KKonstantinov, I think this PR is no longer needed and should be closed due to #1454.
Am I right?