fix: add TX buffer is full check to hasRoom in telemetry

[Elan456]

Description

MARTHA gets stuck if no device is connected for outputting serial data, because the output buffer fills up.
This PR adds a check in telemetry to avoiding adding data to the packet if there wouldn't be enough room for it in the TX buffer.

Summary of Changes

• hasRoom updated to be a member variable and check TX buffer size.

Motivation

• Prevents MARTHA from getting stuck waiting for TX buffer to clear when no devices are connected to the UART port.

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Testing

Check all that apply:

• I have added or modified tests to cover these changes.
• I have manually tested the changes on the target device(s) or environment(s).
• Existing tests were reviewed to ensure they still work as expected.
• If tests were not added or modified, explain why:

  (Provide reasoning here)

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Building

• This change successfully builds in at least one of the following environments:
  • Native repo
  • Target device(s) (e.g., MARTHA)
• If the build fails in any environment, explain why:

  (Provide reasoning here)

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Checklist

• My code follows the style guidelines of this project.
• I have performed a self-review of my own code.
• I have commented my code where necessary for clarity.
• I have made corresponding updates to documentation (if applicable).