Harden generated C runtime behavior and portability

[tolgahan-arikan]

Changes

• make generated client reconfiguration transactional so failed updates preserve the previous working config
• stop automatic redirect following in the generated transport
• harden HTTP response buffering against size_t overflow during large response reads
• add explicit generated runtime hooks around libcurl global initialization and document the contract
• map schema int and uint to int32_t and uint32_t and align decoder bounds with those fixed-width types
• fix enum UNKNOWN round-tripping and reject schema enum values that collide with the reserved sentinel
• add generator and interop regression coverage for transport behavior, runtime setup, numeric widths, enum handling, and config preservation
• regenerate the checked-in smoke example artifacts and update README guidance for the generated runtime

Verification

• go test -count=1 ./...