Acknowledge intentional TrackOutputBytes error design (no-op)

[Copilot]

A reviewer flagged that TrackOutputBytes returns raw sentinel errors rather than wrapping them as *UnmarshalError. This PR closes the loop: the design is intentional — wrapping via unmarshalError (e.g. fmt.Errorf or struct allocation) would push the function's inlining cost past the Go compiler's 80-unit budget (currently 32). Callers retain errors.Is inspectability, and generated code adds context via fmt.Errorf("decoding T: %w", err).

The existing comment at the sentinel declaration already documents this tradeoff:

// Sentinel errors for TrackOutputBytes — using errors.New instead of
// fmt.Errorf keeps the function small enough for the Go compiler to inline.
// Callers wrap these with fmt.Errorf to add context.
var (
    ErrOutputBytesExceeded  = errors.New("output bytes limit exceeded")
    ErrNegativeTrackingSize = errors.New("negative tracking size")
)

No code changes — this PR exists solely to record the design decision and resolve the review thread.

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[tamirms]

Closing — improvements from this PR have been incorporated into #22 where applicable. Thank you!