GH-15137: [C++][CI] Fix ASAN error in streaming JSON reader tests

[benibus]

The input streams passed to the reader weren't properly taking ownership of their test strings, despite the stream (potentially) outliving the test's scope.

• Closes: [C++][CI] ASAN error in streaming JSON reader tests #15137

[github-actions]

• Closes: [C++][CI] ASAN error in streaming JSON reader tests #15137

[github-actions]

⚠️ GitHub issue #15137 has been automatically assigned in GitHub to PR creator.

[pitrou]

Nice one :) Thank you!

[ursabot]

Benchmark runs are scheduled for baseline = a1a587b and contender = a4236ab. a4236ab is a master commit associated with this PR. Results will be available as each benchmark for each run completes.
Conbench compare runs links:
[Finished ⬇️0.0% ⬆️0.0%] ec2-t3-xlarge-us-east-2
[Finished ⬇️1.17% ⬆️0.03%] test-mac-arm
[Failed] ursa-i9-9960x
[Failed] ursa-thinkcentre-m75q
Buildkite builds:
[Finished] a4236abd ec2-t3-xlarge-us-east-2
[Finished] a4236abd test-mac-arm
[Failed] a4236abd ursa-i9-9960x
[Failed] a4236abd ursa-thinkcentre-m75q
[Finished] a1a587b1 ec2-t3-xlarge-us-east-2
[Finished] a1a587b1 test-mac-arm
[Failed] a1a587b1 ursa-i9-9960x
[Failed] a1a587b1 ursa-thinkcentre-m75q
Supported benchmarks:
ec2-t3-xlarge-us-east-2: Supported benchmark langs: Python, R. Runs only benchmarks with cloud = True
test-mac-arm: Supported benchmark langs: C++, Python, R
ursa-i9-9960x: Supported benchmark langs: Python, R, JavaScript
ursa-thinkcentre-m75q: Supported benchmark langs: C++, Java

[ursabot]

['Python', 'R'] benchmarks have high level of regressions.
test-mac-arm