fix: accept test_results as array of glob patterns (align with poetry plugin)

[jimisola]

Problem

The test_results config key in [tool.hatch.build.hooks.reqstool] currently only accepts a bare string:

[tool.hatch.build.hooks.reqstool]
test_results = "build/junit.xml"

This is inconsistent with:

• The poetry plugin, which accepts an array: test_results = ["build/**/junit.xml"]
• The reqstool_config.yml schema, where resources.test_results is an array of strings (glob patterns)

Expected behaviour

Accept an array of glob patterns, consistent with the poetry plugin:

[tool.hatch.build.hooks.reqstool]
test_results = ["build/**/junit.xml"]

Ideally also accept a bare string for backward compatibility (treat it as a single-element array).