fix(rust-ffi): Prevent dangling pointers in copy_from_rust

[cfsmp3]

Summary

• Fixed dangling pointer bug in Rust FFI copy_from_rust() function that caused memory corruption
• Added missing settings_dtvcc.timing = NULL initialization in C's init_options()

Problem

The to_ctype() implementations for DecoderDtvccSettings and Decoder608Settings were creating temporaries on the stack and returning pointers to them:

// In to_ctype():
report: if let Some(value) = self.report {
    &mut value.to_ctype()  // ← Creates temporary, returns dangling pointer!
} else { ... },
timing: &mut self.timing.to_ctype(),  // ← Same issue

When copy_from_rust() called to_ctype(), these dangling pointers were written to the C ccx_options struct. Later when C code tried to use settings_dtvcc.report or settings_dtvcc.timing, it accessed invalid memory.

Valgrind errors before this fix:

Invalid write of size 4
   at 0x1D44ED: dtvcc_init
   Address 0x... is on thread 1's stack, 4016 bytes below stack pointer

Invalid read of size 1
   at 0x32F426: ccx_rust::common::copy_to_rust
   Address 0x... is on thread 1's stack, 1280 bytes below stack pointer

Solution

Preserve the original C-managed pointers instead of overwriting them with dangling pointers:

// Save original C pointers
let saved_report = (*ccx_s_options).settings_dtvcc.report;
let saved_timing = (*ccx_s_options).settings_dtvcc.timing;

// Apply other fields from to_ctype()
(*ccx_s_options).settings_dtvcc = options.settings_dtvcc.to_ctype();

// Restore the C-managed pointers
(*ccx_s_options).settings_dtvcc.report = saved_report;
(*ccx_s_options).settings_dtvcc.timing = saved_timing;

Test plan

• Verified all 21 Teletext tests pass (tests 63-83)
• Verified test 18 and 19 pass with exit code 0
• Verified valgrind no longer reports "Invalid read/write" errors
• Error summary reduced from 131,099 errors (15 contexts) to 131,074 errors (4 contexts) - the remaining warnings are unrelated uninitialized memory issues

🤖 Generated with Claude Code