Fix HTTP instrumentation for http gem v6.0+

[lancetarn]

Summary

• Fixes HTTP instrumentation incompatible with http gem v6.0 #613 — ArgumentError: wrong number of arguments (given 3, expected 2) when using http gem v6.0+
• http gem v6.0 changed HTTP::Client#request from positional args (verb, uri, opts = {}) to keyword args (verb, uri, **opts)
• Adds version detection via Gem::Version and separate instrumentation paths for v5 (positional) and v6+ (keyword) in both the prepend and alias code paths

Test plan

• Existing HTTP instrumentation test updated and passes with http gem v6.0.2
• Full test suite (284 tests) passes with no regressions
• Verify with http gem v5.x to confirm backwards compatibility

🤖 Generated with Claude Code

[kjanoudi]

We hit the same incompatibility in production after upgrading to http 6.

Our environment:

• scout_apm 6.1.1
• http 6.0.2
• Ruby 3.4.7
• Rails 8.0.2.1

Observed error:
ArgumentError: wrong number of arguments (given 3, expected 2)

One failing path for us was a Sidekiq job calling HTTP.get(..., params: ...) through IpInfo.fetch_ipstack, but we also found other backend HTTP calls using params:, json:, and form: that would go through the same Scout wrapper.

We applied a local compatibility patch that forwards **opts in both the alias and prepend instrumentation paths, and that resolved the issue for us. So this PR matches what we needed downstream.

Thanks for putting this together.