chore: Prepare release 1.2.0

[TheRealAgentK]

Release branch PR for 1.2.0

Description 📝

• Purpose: Updates Changelog and version to 1.2.0

Type of change

• Release

Updates

👉 Bump version to 1.2.0 in pubspec.yaml and bin/raygun_cli.dart
👉 Update CHANGELOG.md with changes since 1.1.0

Changes in this release

• chore(deps): bump lints from 6.0.0 to 6.1.0, use null-aware elements (chore(deps): bump lints from 6.0.0 to 6.1.0 #46)
• chore(deps): bump test from 1.28.0 to 1.29.0 (chore(deps): bump test from 1.28.0 to 1.29.0 #47)
• chore(deps): bump build_runner from 2.10.4 to 2.10.5 (chore(deps): bump build_runner from 2.10.4 to 2.10.5 #48)
• chore(deps): bump mockito from 5.6.1 to 5.6.3 (chore(deps): bump mockito from 5.6.1 to 5.6.3 #49)
• chore: upgrade transitive dependencies (chore: upgrade transitive dependencies #50)

Test plan 🧪

• dart analyze - passes with no issues
• dart test - all 58 tests pass
• dart compile exe bin/raygun_cli.dart - builds 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)