Fix TRACE_enable panic on missing file to match C fopen append behavior

[heroicpixel]

Description

Fixes #312

Changes

• File Creation Parity: Added .create(true) to OpenOptions in programs/zstdcli_trace.rs. This ensures that opening a trace log file with --trace automatically creates the file if it does not exist, matching C's fopen(..., "a") append behavior and resolving the runtime panic on fresh runs.

Verification

Verified locally that running zstdcli on a fresh run successfully creates trace.log, writes the CSV header row, and captures compression metrics without panicking.

PR was supported by AI.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
programs/zstdcli_trace.rs	0.00%	1 Missing ⚠️

Flag	Coverage Δ
test-aarch64-apple-darwin	33.03% <0.00%> (-0.02%)	⬇️
test-aarch64-unknown-linux-gnu	31.63% <0.00%> (-0.01%)	⬇️
test-i686-unknown-linux-gnu	31.69% <0.00%> (-0.01%)	⬇️
test-x86_64-unknown-linux-gnu	33.34% <0.00%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
programs/zstdcli_trace.rs	0.00% <0.00%> (ø)

... and 3 files with indirect coverage changes

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