Fix non-deterministic example generation for additionalProperties when schemaFaker is disabled

[Aggarwalmansi]

Problem

When converting OpenAPI schemas using openapi-to-postmanv2, setting
schemaFaker: false is expected to produce deterministic examples.

Currently, schemas that contain additionalProperties still result in
random property names and values being generated across runs (for example,
amet_04, sit_2, etc.). This makes the output non-deterministic even
when schema faking is explicitly disabled.

This is most noticeable for object schemas that rely on
additionalProperties rather than explicitly defined fields.

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Root Cause

While schemaFaker is disabled, example generation for object schemas
with additionalProperties still falls back to faker-based logic.
As a result, random keys and values are produced instead of stable
schema placeholders.

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Solution

This change adds a deterministic fallback for object schemas that use
additionalProperties when schemaFaker is set to false.

• Faker-based generation is skipped in this case
• A stable placeholder object (for example "<property>": "<string>")
  is returned instead
• Existing behavior remains unchanged when schemaFaker is enabled
• Schemas without additionalProperties are not affected

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Impact

This ensures consistent and repeatable Postman collections when
schemaFaker: false is used, avoiding unnecessary diffs and improving
reliability in CI/CD and version-controlled workflows.

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Related Issue

Fixes #854