🏗️ Architect: Centralize NotFoundError across GET Endpoint Mixins

[fderuiter]

🏗️ Design Change:

Replaced generic ValueError exceptions with custom NotFoundErrors from imednet.errors.api across API get request mixins (FilterGetEndpointMixin, PathGetEndpointMixin) and specific endpoint overrides (JobsEndpoint).

♻️ DRY Gains:

Ensures a single, consistent Exception path (NotFoundError) for all single-item retrieval failures across the entire SDK.

🛡️ Solidity:

Enhances API robustness and adheres to the established exception hierarchy, preventing leaky abstractions where users would have had to catch base Python ValueErrors rather than specific ImednetError derivatives.

⚠️ Breaking Changes:

Clients who strictly caught ValueError specifically for "Not Found" logic on .get() methods will now need to catch NotFoundError (or the base ApiError/ImednetError).

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PR created automatically by Jules for task 12475786350183174156 started by @fderuiter

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