Make mcpb package version optional and fix schema validation (#686)

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## Motivation and Context
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The following PR:
* Makes mcpb package version property optional
* Bumps the schema and reflects that in the code
* Makes sure the publisher tests are being covered by doing `make check`

## How Has This Been Tested?
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tested? -->

## Breaking Changes
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## Types of changes
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the boxes that apply: -->
- [ ] 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
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that apply. -->
- [ ] I have read the [MCP
Documentation](https://modelcontextprotocol.io)
- [ ] 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
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---------

Signed-off-by: Radoslav Dimitrov <radoslav@stacklok.com>

pkg/api/v0/types.go

@@ -32,7 +32,7 @@ type ServerMeta struct {
 }
 
 type ServerJSON struct {
-	Schema      string            `json:"$schema" required:"true" minLength:"1" format:"uri" doc:"JSON Schema URI for this server.json format" example:"https://static.modelcontextprotocol.io/schemas/2025-09-29/server.schema.json"`
+	Schema      string            `json:"$schema" required:"true" minLength:"1" format:"uri" doc:"JSON Schema URI for this server.json format" example:"https://static.modelcontextprotocol.io/schemas/2025-10-17/server.schema.json"`
 	Name        string            `json:"name" minLength:"3" maxLength:"200" pattern:"^[a-zA-Z0-9.-]+/[a-zA-Z0-9._-]+$" doc:"Server name in reverse-DNS format. Must contain exactly one forward slash separating namespace from server name." example:"io.github.user/weather"`
 	Description string            `json:"description" minLength:"1" maxLength:"100" doc:"Clear human-readable explanation of server functionality." example:"MCP server providing weather data and forecasts via OpenWeatherMap API"`
 	Title       string            `json:"title,omitempty" minLength:"1" maxLength:"100" doc:"Optional human-readable title or display name for the MCP server." example:"Weather API"`