19212: shell/rtc: use rtc_tm_normalize() to sanitize input r=benpicco a=benpicco
19360: gcoap: make use coap_build_reply() in gcoap_resp_init() r=benpicco a=benpicco
19401: shell/cmds: add genfile command r=benpicco a=benpicco
19645: sys/isrpipe: Replace xtimer with ztimer_usec r=benpicco a=MrKevinWeiss
### Contribution description
Getting ready for the xtimer dep.
### Testing procedure
Green murdock, there is no explicit test for isrpipe but since it runs xtimer compat it should operate the same.
### Issues/PRs references
19720: tests: remove unnecessary use of floating point r=benpicco a=benpicco
Co-authored-by: Benjamin Valentin <benjamin.valentin@bht-berlin.de>
Co-authored-by: Benjamin Valentin <benjamin.valentin@ml-pa.com>
Co-authored-by: MrKevinWeiss <weiss.kevin604@gmail.com>
Co-authored-by: Benjamin Valentin <benpicco@beuth-hochschule.de>
- Replace all users of `$(RIOTBASE)/build` with the already present
`$(BUILD_DIR)` variable
- Replace all users of `$(BUILD_DIR)/pkg` with the already present
`$(PKGDIRBASE)` variable
- Create a `CACHEDIR.TAG` file in the `$(BUILD_DIR)`
