chore: Prepare release 1.2.1

[TheRealAgentK]

chore: Prepare release 1.2.1

Description 📝

• Purpose: Release 1.2.1 with updated dev dependencies from merged dependabot PRs.
• Approach: Bump version to 1.2.1 in pubspec.yaml and bin/raygun_cli.dart, update CHANGELOG.md.

Type of change

• This change requires a documentation update

Updates

👉 chore(deps): bump test from 1.29.0 to 1.30.0 (#53)
👉 chore(deps): bump build_runner from 2.10.5 to 2.11.1 (#54)
👉 Version bumped to 1.2.1 in pubspec.yaml, bin/raygun_cli.dart, and CHANGELOG.md

Test plan 🧪

• All 58 tests pass (dart test)
• dart analyze — no issues found
• dart format — no changes needed
• dart compile exe — compiles successfully

Author to check 👓

• Project and all contained modules builds successfully
• Self-/dev-tested
• Unit/UI/Automation/Integration tests provided where applicable
• Code is written to standards
• Appropriate documentation written (code comments, internal docs)

Reviewer to check ✔️

• Project and all contained modules builds successfully
• Change has been dev-/reviewer-tested, where possible
• Unit/UI/Automation/Integration tests provided where applicable
• Code is written to standards
• Appropriate documentation written (code comments, internal docs)