perf(swc_ts_fast_strip): skip comment collection in strip-only mode

[kdy1]

Summary

Strip-only mode appears to collect parser comments even though comments are not used in that mode.

Evidence

• Comments storage is always initialized: crates/swc_ts_fast_strip/src/lib.rs:246.
• Lexer always receives Some(&comments): crates/swc_ts_fast_strip/src/lib.rs:248-253.
• In Mode::StripOnly, output is produced by mutating the original source bytes; no comment map is consulted.

Why this is a performance risk

Comment collection adds parser-side bookkeeping and memory overhead on every strip-only call, even though the comment data is unused on that path.

Suggested direction

• Pass None for comments when running strip-only mode.
• Keep comment collection for transform mode where fixer/codegen paths may rely on comment metadata.

Benchmark idea

Measure strip-only throughput and allocations before/after disabling comment collection for strip-only.