Ruby 3.3 managed runtime pre-activates bigdecimal 4.0.1, causing Gem::LoadError for bigdecimal 3.x

## Description
We received a customer report on the AWS SDK for Ruby repo [aws-sdk-ruby#3273](https://github.com/aws/aws-sdk-ruby/pull/3273#issuecomment-4344619239)) about a bigdecimal version conflict on the Ruby 3.3 managed Lambda runtime.

In July 2025, the `aws-sdk-core` gem declares bigdecimal as a runtime dependency (with no version constraint). The runtime (ruby:3.3.mainline.v94) appears to pre-activate bigdecimal 4.0.1 as a default gem.

The stack trace contains no SDK or application frames: it's entirely Bundler and Lambda runtime code.

Could you take a look and let us know what the best path forward is?

## Customer Context
```

{
"errorMessage": "You have already activated bigdecimal 4.0.1, but your Gemfile requires
bigdecimal 3.1.8. Prepending `bundle exec` to your command may solve this.",
"errorType": "Init",
"stackTrace": [
"/var/lang/lib/ruby/site_ruby/3.3.0/bundler/runtime.rb:328:in `check_for_activated_spec!'",
"/var/lang/lib/ruby/site_ruby/3.3.0/bundler/runtime.rb:25:in `block in setup'",
"/var/lang/lib/ruby/site_ruby/3.3.0/bundler/spec_set.rb:224:in `each'",
"/var/lang/lib/ruby/site_ruby/3.3.0/bundler/spec_set.rb:224:in `each'",
"/var/lang/lib/ruby/site_ruby/3.3.0/bundler/runtime.rb:24:in `map'",
"/var/lang/lib/ruby/site_ruby/3.3.0/bundler/runtime.rb:24:in `setup'",
"/var/lang/lib/ruby/site_ruby/3.3.0/bundler.rb:165:in `setup'",
"/var/lang/lib/ruby/site_ruby/3.3.0/bundler/setup.rb:32:in `block in '",
"/var/lang/lib/ruby/site_ruby/3.3.0/bundler/ui/shell.rb:177:in `with_level'",
"/var/lang/lib/ruby/site_ruby/3.3.0/bundler/ui/shell.rb:122:in `silence'",
"/var/lang/lib/ruby/site_ruby/3.3.0/bundler/setup.rb:32:in `'",
"/var/runtime/gems/aws_lambda_ric-3.1.3/lib/aws_lambda_ric.rb:46:in `run'",
"/var/runtime/gems/aws_lambda_ric-3.1.3/lib/aws_lambda_ric.rb:219:in `bootstrap_handler'",
"/var/runtime/gems/aws_lambda_ric-3.1.3/lib/aws_lambda_ric.rb:201:in `start'",
"/var/runtime/index.rb:4:in `'"
]
}
```

Managed zip. Here's the INIT line from the logs:
> INIT_START Runtime Version: ruby:3.3.mainline.v94 Runtime Version ARN: arn:aws:lambda:us-east-1::runtime:58713c1f627a6d04dfda3ea4e11fae1cbca3ac46a4becad26f739c38911423d9