Update EnumSchema and extend Elicitation result to support string array return type. See [SEP-1330](modelcontextprotocol/modelcontextprotocol#1330)

* In types.ts
  - add UntitledSingleSelectEnumSchema, TitledSingleSelectEnumSchema, LegacyTitledEnumSchema
    - add SingleSelectEnumSchema that is a union of these three
  - add UntitledMultiSelectEnumSchema, TitledMultiSelectEnumSchema
    - add MultiSelectEnumSchema that is a union of these two
  - refactor EnumSchemaSchema to be a union of SingleSelectEnumSchema and MultiSelectEnumSchema

* In elicitation.test.ts
  - simplify tests by extracting the duplicated client and server creation and connection into a beforeEach run in the describe for each flow
  - add positive/negative tests for all enum permutations (single-select, multi-select, titled, untitled, and legacy
    - "should succeed with valid selection in single-select untitled enum"
    - "should succeed with valid selection in single-select titled enum"
    - "should succeed with valid selection in single-select titled legacy enum"
    - "should succeed with valid selection in multi-select untitled enum"
    - "should succeed with valid selection in multi-select titled enum"
    - "should reject invalid selection in single-select untitled enum"
    - "should reject invalid selection in single-select titled enum"
    - "should reject invalid selection in single-select titled legacy enum"
    - "should reject invalid selection in multi-select untitled enum"
    - "should reject invalid selection in multi-select titled enum"

Author: cliffhall