chore(config): migrate tracer.ciVisibilityEnabled

[mtoffl01]

What does this PR do?

Tracer migrates to using Config.ciVisibilityEnabled instead of its own config.ciVisibilityEnabled.

Motivation

datadoghq.atlassian.net/browse/APMAPI-1748

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 ./scripts/lint.sh 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.

Unsure? Have a question? Request a review!

[pr-commenter]

Benchmarks

Benchmark execution time: 2025-12-10 17:16:38

Comparing candidate commit 744a237 in PR branch mtoff/ciVisibilityEnabled with baseline commit 1a6f881 in branch main.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 15 metrics, 0 unstable metrics.

[codecov]

Codecov Report

❌ Patch coverage is 15.78947% with 16 lines in your changes missing coverage. Please review.
✅ Project coverage is 54.35%. Comparing base (1a6f881) to head (744a237).

Files with missing lines	Patch %	Lines
internal/config/config.go	13.33%	13 Missing ⚠️
ddtrace/tracer/tracer.go	0.00%	0 Missing and 2 partials ⚠️
ddtrace/tracer/option.go	0.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

Files with missing lines	Coverage Δ
ddtrace/tracer/stats.go	98.46% <100.00%> (ø)
ddtrace/tracer/option.go	85.33% <0.00%> (+0.71%)	⬆️
ddtrace/tracer/tracer.go	86.40% <0.00%> (+0.19%)	⬆️
internal/config/config.go	71.01% <13.33%> (-28.99%)	⬇️

... and 69 files with indirect coverage changes

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