envoyproxy: fix partial parsing jsoniter truncated map key

[e-n-0]

What does this PR do?

This PR fixes an issue in partial‐parsing mode where a truncated map key would wrongly trigger an error, ensuring that such keys no longer cause failures.

Motivation

Error in partial parsing.

Reviewer's Checklist

• [ ] Changed code has unit tests for its functionality at or near 100% coverage.
• [ ] System-Tests covering this feature have been added and enabled with the va.b.c-dev version tag.
• [ ] There is a benchmark for any new code, or changes to existing code.
• [ ] If this interacts with the agent in a new way, a system test has been added.
• [ ] New code is free of linting errors. You can check this by running golangci-lint run locally.
• [ ] Add an appropriate team label so this PR gets put in the right place for the release notes.
• [ ] Non-trivial go.mod changes, e.g. adding new modules, are reviewed by @DataDog/dd-trace-go-guild.

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[pr-commenter[bot]]

Benchmarks

Benchmark execution time: 2025-06-25 11:34:02

Comparing candidate commit 36823dbea3a592a954f622081bbe93dc25761d81 in PR branch flavien/jsoniter/fix-truncated-map-key with baseline commit deedd5b5cf537fa9c06cac1952b8bdf90d36acd6 in branch main.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 24 metrics, 0 unstable metrics.

[datadog-datadog-prod-us1[bot]]

Datadog Report

Branch report: flavien/jsoniter/fix-truncated-map-key Commit report: 4d70c1e Test service: dd-trace-go

:white_check_mark: 0 Failed, 70 Passed, 0 Skipped, 4m 22.93s Total Time