Beta release 1.9.0-beta.3

[tabemann]

This beta release adds string,, string@, and string! for conveniently compiling string constants and reading and writing strings without the constraints of traditional counted strings, updates endof, endcase, and endcasestr on the RP2350, STM32F407, STM32F411, and STM32F746 for all branches at the ends of of ... endof blocks to point to the end of the case ... endcase/endcasestr block (the RP2040 and STM32L476 are not so updated due to the platforms' limitations), adds task-deadline! and task-deadline@ in the task module to allow finer control over the deadline scheduler, and tunes zeptoIP to take advantage of the deadline scheduler.

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This discussion was created from the release Beta release 1.9.0-beta.3.