feat: decode composite (vec/map) call arguments; raise recursion limit

[RaoulSchaffranek]

Summary

Two fixes that surfaced while debugging a real Soroban contract through the komet-node-backed debugger.

1. Composite (Vec/Map) call arguments

komet-node rejected any Vec/Map — and therefore any user enum, struct, or tuple — contract call argument at admission: scval_to_json raised NotImplementedError on SCV_VEC/SCV_MAP, and the #decodeArg rules had only scalar cases, so sendTransaction failed with txMALFORMED and the invocation never ran.

This adds recursive vec/map support on both sides:

• scval.py — scval_to_json emits {"type":"vec","value":[…]} and {"type":"map","value":[{"key":…,"val":…},…]}, recursing element-wise. - node.md — #decodeArg vec/map rules: ScVec(#decodeArgList(…)) and ScMap(#decodeMapEntries(…)). Enums, structs, and tuples all reduce to vec/map at the XDR level, so these two rules cover every composite argument.

Verified end-to-end (test_call_tx_with_composite_args): a contract call carrying a flat vec, a nested Vec<(enum, i128)> (with an Address-carrying variant and a negative i128), a struct-shaped map, and a map-nested-in-vec reaches SUCCESS, and the arguments echoed in the trace's callContract frame round-trip back to the exact SCVals that were sent — so a decoding bug is caught even when the transaction still succeeds (same style as the existing test_call_tx_with_args).

2. Recursion limit for large real contracts

Large real contracts produce a KORE world-state term far deeper than CPython's default recursion limit (1000), which surfaced as a RecursionError mid-request during pyk's recursive-descent KORE parsing / config traversal.

• __init__.py — sys.setrecursionlimit(10**7), matching the rest of the
  K tooling (pyk sets 10**7; komet sets its own limit at import).
• server.py — run the blocking serve loop on a worker thread with a
  512 MB stack, so a deep term raises a catchable RecursionError rather than
  overflowing the 8 MB default stack into a SIGSEGV (keeping the server's
  "never take down the serve thread" guarantee intact).
• test_scval.py — unit tests pinning the vec/map JSON shape
  (order-sensitive, since #decodeArg matches on JSON member order) and that a
  deeply nested value encodes without hitting the recursion limit.

Testing

• Full suite green after a kdist rebuild: 97 passed.
• make check clean: flake8, mypy (24 files), black, isort.

Notes

The two changes are independent and can be split into separate PRs if preferred; they are bundled here because both came out of the same debugging session. Developed test-first (red proven before green).