fix(jobs): integrate zod schema middleware with validateWithFields in…

[Davoski1]

Description

Closes #115

This PR integrates Zod request shape validations as a reusable middleware handler for the POST /api/jobs/:contractId/milestones/:index/partial-release route, enabling detailed field-level validation errors.

Changes Made

• Middleware Update: Replaced the validate middleware with validateWithFields for the partialReleaseBodySchema inside src/routes/jobs.ts. This ensures that invalid request shapes are parsed and reported back with a fields mapping (e.g., fields: { amount: "..." }) rather than just a generic array of error details.
• Test Coverage: Updated existing validation tests in __tests__/partial-release.test.ts to assert that the new fields property is correctly returned in the JSON response payload for invalid formats (e.g. invalid amount or sourceAddress).

Verification

• All 25 test cases for the partial-release endpoint pass successfully.
• Invalid formats are properly caught, parsed, and reported back as specific field validation errors.
• Code conforms to the existing repository patterns (linting, formatting, typings).