Use default `max_lines` when calling `up` & `down`

[HeyNonster]

Description

Both up and down only show 1 source line when called, I think it would be more useful if they provided more context. This removes the max_lines: 1 kwarg when they call show_src. max_lines in show_src will default to CONFIG[:show_src_lines]^1.

Big thanks to @st0012 for showing me and @bquorning where this behavior is defined.

[st0012]

I want to second this proposal as I also often need to chain whereami after moving to a different frame, which IMO is not the best user experience in most cases.

[HeyNonster]

Also probably useful to note that byebug displays more lines by default making it quite a difference switching from byebug to debug:

https://github.com/ruby/debug/assets/47484308/5f2174b9-1264-4753-be71-14203977c69f

[launchable-app[bot]]

Launchable Report

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_{:bell: no issues :heavy_multiplication_x:1 test failed :heavy_check_mark:63 tests passed}

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_{:bell: no issues :heavy_multiplication_x:1 test failed :heavy_check_mark:63 tests passed}

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Build: refs_pull_1094_merge_b1963e7b72554c9672900ba046c3088598955488

[HeyNonster]

Seems the protocol tests are flaky: https://github.com/ruby/debug/pull/1060

[ko1]

Maybe we need to introduce another configuration.