feat: add ConnTimeout option, improve GenId entropy and refine logging

[luopengift]

options.go / transport.go:

• Add field (default 10s) to Options for configuring TCP dial timeout independently from the overall request
• Pass to socket dialer instead of hard-coded value
• Add doc note warning that unix:// path is session-level only

stat.go / trace.go / response.go / request.go:

• Refactor Stat struct fields and Print/String output format
• Add response body truncation in LogS (cap at 1024 chars) and drop redundant json.Marshal path; use a2s helper uniformly

uid.go:

• Switch GenId from nanosecond to microsecond precision multiplied by 1000 to cleanly separate time bits from random bits, reducing collision risk under high concurrency while staying within uint64

util.go:

• Remove unused encoding/json import
• Simplify LogS body logging via a2s helper with 1024-byte truncation

requests_test.go / request_test.go / response_test.go / stat_test.go:

• Update and extend tests to cover new fields, LogS truncation, GenId uniqueness, and revised Stat output format