Bump to 1.2.5

[Bitflash-sh]

Version bump for v1.2.5.

Why this release matters: #42. -gen has mined nothing on headless nodes since v1.2.0 — nMineMode stayed at MINE_RELAY and BitcoinMiner() returned immediately without logging anything. Anyone running a headless miner on v1.2.0 through v1.2.4 has an idle CPU and no indication of it.

Since v1.2.4:

• main: make /gen actually mine #42 — /gen actually mines (ericscalibur)
• sha: restrict the x86 bswap asm to x86 #41 — x86 bswap asm no longer breaks ARM64 builds (ericscalibur)
• gitignore: cover the key files the node actually writes #43 — .gitignore covers btf_enc.key, nostr.key, walletrpc.token (ericscalibur)
• build: check format strings, which nothing ever did #44 — format strings are checked at build time; fixes the class of bug behind Segfault at block 1062 on Linux headless #5, plus a truncated-pointer log line and a mangled error message

Verified on the merged tree, both platforms: clean build, nMineMode = 1 with BitcoinMiner started and RandomX in fast mode, repaired log lines correct, no crash.