.Net: Add backslash escaping to redis text search values

[westey-m]

Motivation and Context

Description

• Add backslash escaping to redis text search values

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the SK Contribution Guidelines and the pre-submission formatting script raises no violations
• All unit tests pass, and I have added new tests where possible
• I didn't break anyone 😄

[github-actions]

Automated Code Review

Reviewers: 3 | Confidence: 94% | Result: All clear

Reviewed: Correctness, Security Reliability, Test Coverage

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Automated review by westey-m's agents

[Copilot]

Pull request overview

Adds additional escaping for RedisSearch exact-match/tag query string values so that literal backslashes in user-provided filter values are preserved and can’t be interpreted as escape characters in the query syntax.

Changes:

• Update SanitizeStringConstant to escape backslashes (\ → \\) before escaping double quotes.
• Add unit tests covering backslashes and backslash+quote “injection-style” payloads for ==, Contains, and Any(...Contains...).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
dotnet/src/VectorData/Redis/RedisFilterTranslator.cs	Escapes backslashes in string constants before generating RedisSearch query fragments.
dotnet/test/VectorData/Redis.UnitTests/RedisFilterTranslatorTests.cs	Adds regression tests to validate correct escaping for backslashes in multiple translation paths.

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