ETR01SDK-563: Mention that lt_deinit and lt_init has to be called after FW update

[medexs]

Description

Adds mentions about the need of reinitializing the handle after a successful call of lt_do_mutable_fw_update.

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Type of Change

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• 🐛 Bug fix
• ✨ New feature
• 🧹 Code cleanup or refactoring
• 📝 Documentation update
• 🔧 Build system or toolchain update
• 🔒 Security improvement
• Other (please describe):

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Checklist

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• I opened the Pull Request to the develop branch
• I followed the project's code guidelines
• I formatted the code using clang-format with the recommended configuration
• I updated the changelog, or this change does not require it (e.g., internal or non-functional update)
• The project builds without errors or warnings
• I have verified the functionality against the hardware/model as applicable
• I have ensured that public APIs remain backward compatible (if applicable)
• This PR is ready for review by maintainers (no WIP commits left) and marked as Ready for Review

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[Copilot]

Pull request overview

Updates public API and example documentation to clarify that the libtropic handle must be reinitialized after a successful mutable firmware update.

Changes:

• Add a note to lt_do_mutable_fw_update() API docs about reinitializing the lt_handle_t after a successful update.
• Add an MkDocs info callout in the firmware update example documentation describing the same requirement.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
include/libtropic.h	Adds a highlighted note to the lt_do_mutable_fw_update() Doxygen comment about reinitializing the handle after successful FW update.
docs/common/examples_descriptions/fw_update.md	Adds an info admonition reminding application developers to reinitialize the handle after lt_do_mutable_fw_update() succeeds.

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