Allow using library in CurrentThread runtime

[sgrebnov]

The block_in_place function requires a multi-threaded runtime and will crash when executed in CurrentThread mode, which is the default for unit tests. While unit tests can be configured to run in multi-threaded mode, this is sometimes not practical or may require a significantly more complex setup, especially when tests involve tracing collectors.

With this change, the dummy run is skipped in single-threaded environments, simplifying the setup for unit tests.

[github-actions]

Code Metrics Report

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 Language            Files        Lines         Code     Comments       Blanks
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 Jupyter Notebooks       4            0            0            0            0
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 (Total)                            282          210           32           40
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 Markdown               46         3802            0         2891          911
 |- BASH                 6          103          100            0            3
 |- JSON                 1           12           12            0            0
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 (Total)                           4625          717         2891         1017
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 Rust                  309        99535        89232         1924         8379
 |- Markdown           149         1688           25         1538          125
 (Total)                         101223        89257         3462         8504
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 Total                 467       110873        92517         7337        11019
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[EricLBuehler]

Thank you, looks great.