avm2: Make PerspectiveProjection.focalLength more precise #27679

Job	Run time
Paths filter	10s
Lints with Rust beta	3m 53s
Lints with Rust nightly	3m 53s
Test Rust stable / windows-latest	11m 2s
Test Rust beta / ubuntu-24.04	4m 45s
Test Rust nightly / ubuntu-24.04	8m 26s
Test Rust stable / ubuntu-24.04	4m 45s
Lints with Rust stable	3m 37s
Test Rust stable / macos-14	4m 0s
Check dependencies	1m 25s
format('Test Rust {0} / {1}', matrix.rust_version, matrix.os)	0s
	45m 56s

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