Make rmm a compiled rather than header-only library

[vyasr]

rmm is currently a header-only library. This design has been convenient for a long time, but so far as we know it is not a hard requirement for any consumer. Conversely it has some drawbacks.

• Using rmm as a header-only library limits our ability to manage symbol visibility due to inline symbols, something that is becoming increasingly important as we distribute more general packages.
• Since we attempt to also keep our dependency tree header-only, the same symbol limitations apply to our dependencies, specifically spdlog and fmt.
• With a header-only library we are also effectively tied to the ABI (in)stability of the projects that we depend on, whereas with a precompiled library we could hide those details behind a suitable implementation firewall.
• Our reliance on the uniqueness of function-local statics across shared library boundaries precludes the possibility of building rmm on Windows.

Many of these issues are made particularly evident by the ongoing work on rapids-logger, which is in large part motivated by a desire to insulate RAPIDS from both spdlog's ABI changes and exposing its symbols publicly. As we are upstreaming much of rmm's core functionality into CCCL, which is header-only, I anticipate that converting rmm to a precompiled library will not be a major long-term issue, and it will help resolve these classes of problems.

I propose that we start shipping rapids-logger artifacts in 25.04, at which point rmm may still be header-only but will have a library dependency. Depending on the timing of other work, we can convert rmm to a precompiled library in either 25.04 or 25.06.