fix: [CN-68] update TEXT and JSON encoders to correctly handle nil input

[vpakhuchyi]

Pull request

Link to the related ticket

https://censor.atlassian.net/browse/CN-68

Description of changes

Update TEXT and JSON encoders to correctly handle nil input.

Checklist

Please ensure that your pull request complies with the following requirements:

• The changes have been tested locally (if applicable).
• The documentation has been updated (if applicable).

[Copilot]

Pull Request Overview

This PR refactors nil value handling by moving the logic from the Processor.Any method into the individual encoders (TEXT and JSON), ensuring each encoder handles invalid reflect.Value objects appropriately.

Key Changes:

• Removed nil check from Processor.Any() method
• Added !f.IsValid() checks to both TEXT and JSON encoder Encode() methods
• Added comprehensive test coverage for nil handling with both encoder types

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
processor.go	Removed nil check from Processor.Any() method, delegating responsibility to encoders
internal/encoder/text_encoder.go	Added nil/invalid value check at the start of Encode() method, returning "nil" for TEXT format
internal/encoder/json_encoder.go	Added nil/invalid value check at the start of Encode() method, returning "null" for JSON format
processor_test.go	Added test cases for nil value handling with both JSON (default) and TEXT encoders

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