Enhancements and fixes to autocomplete behaviour

[bdavj]

Description

Autocomplete behaviour enhancements and fixes to remedy issues with repeat requests and timeouts (#4413).

• Re-surfacing control within the user configuration GUI for debounce delay
• Adding control within user configuration for autocomplete model timeout
• Fixing issues around debounce delay whereby

Screenshots

Testing Instructions

Configuration Verification

• Open user configuration GUI
• Verify presence of new debounce delay and timeout controls
• Confirm settings are persisted after modification

Functionality Testing

• Set various debounce delays and observe completion timing
• Test with longer model timeouts for complex completions
• Verify multi-line completions display correctly

Validation Steps

• Monitor .continue/prompt.log for completion responses
• Confirm completions only trigger after configured debounce delay
• Verify all lines of multi-line completions appear in IDE

Edge Cases

• Test with minimal and maximum timeout values
• Verify behavior with rapid consecutive typing
• Check completion behavior across different file types

Related Issues

• Fixes #4413 - Autocomplete timing and multi-line display issues