Ryan Malloy 12b0a231f0 Implement Specctra SES session-file writer
Ports the write path of io/specctra/SesWriter.java to emit a valid
session from a parsed DsnBoard plus a RoutingResult. Each _write_*
function mirrors a write* method upstream:

- session scope with base_design, placement (resolution + components
  echoed from the DSN), an empty was_is, and routes
- routes carries resolution, a reduced parser scope, library_out with
  the via padstacks, and network_out
- network_out emits (net (wire (path layer width x1 y1 ...)) (via
  padstack x y)) for each routed net; integer coordinates via round-
  half-up to match Java Math.round

write_ses(board) with no result produces a valid no-op session,
proving the DSN-in / SES-out round trip. Only routes > network_out is
required by SesReader and kicad-cli; the rest is echoed for a
well-formed file.

18 tests: indent/quoting rules, no-op session structure, placement and
library_out echo, routed wire/via serialization, integer rounding, and
round-trips re-parsed through the project's own DSN tokenizer/sexp
(64 tests total across the suite, all green; ruff clean).
2026-07-11 16:34:19 -06:00
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