chore(di): add @key and @value to collection expressions

[P403n1x87]

We add the @key and @value special identifier to allow users to refer to keys and values from a dict-like object.

Checklist

• PR author has checked that all the criteria below are met
• The PR description includes an overview of the change
• The PR description articulates the motivation for the change
• The change includes tests OR the PR description describes a testing strategy
• The PR description notes risks associated with the change, if any
• Newly-added code is easy to change
• The change follows the library release note guidelines
• The change includes or references documentation updates if necessary
• Backport labels are set (if applicable)

Reviewer Checklist

• Reviewer has checked that all the criteria below are met
• Title is accurate
• All changes are related to the pull request's stated goal
• Avoids breaking API changes
• Testing strategy adequately addresses listed risks
• Newly-added code is easy to change
• Release note makes sense to a user of the library
• If necessary, author has acknowledged and discussed the performance implications of this PR as reported in the benchmarks PR comment
• Backport labels are set in a manner that is consistent with the release branch maintenance policy

[github-actions]

CODEOWNERS have been resolved as:

ddtrace/debugging/_expressions.py                                       @DataDog/debugger-python
tests/debugging/test_expressions.py                                     @DataDog/debugger-python

[datadog-dd-trace-py-rkomorn]

Datadog Report

Branch report: chore/di-expr-key-value-dict
Commit report: 6d744a2
Test service: dd-trace-py

✅ 0 Failed, 130 Passed, 1468 Skipped, 4m 28.42s Total duration (35m 34.78s time saved)

[pr-commenter]

Benchmarks

Benchmark execution time: 2025-01-22 16:41:16

Comparing candidate commit 6d744a2 in PR branch chore/di-expr-key-value-dict with baseline commit cd6422a in branch main.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 394 metrics, 2 unstable metrics.