Spoom fails when a BUNDLE_PATH is set

Describe the bug
Spoom ignores the BUNDLE_PATH when trying to bundle exec srb.

To Reproduce
Spoom version: 1.2.4

Steps to reproduce the behavior:

1. Set a BUNDLE_PATH
2. Run bundle exec spoom tc
3. You'll get an error along the lines of:

bundler: failed to load command: srb (/app/bundle/bin/srb)
/usr/local/lib/ruby/3.1.0/bundler/source/git.rb:214:in rescue in load_spec_files': https://github.com/crafterm/apnotic.git (at e0a84c9@e0a84c9) is not yet checked out. Run bundle install first. (Bundler::GitError)

The above error is from a Docker instance in our CI environment, with BUNDLE_PATH set to /app/bundle and spoom being executed in /app/api. The particular error will depend on your bundle path and gems, but it'll always tell you it can't find your gems and that you need to bundle install.

Expected behavior
Spoom should respect the BUNDLE_PATH and successfully execute srb.

The code
This code is what causes the problem. Spoom removes the entire bundler environment and then re-runs bundle exec.

I would expect Spoom and Sorbet to always be in the same bundle, so you shouldn't need to re-run bundle exec. Maybe there's a use case I'm not thinking of though?

Start at lib/spoom/context/exec.rb around line 36, where Spoom clears the Bundler environment and invokes bundle exec. Reproduce the problem with BUNDLE_PATH set and bundle exec spoom tc, then verify that the command can execute srb using the configured bundle without the missing-gems error.