Add tests for CHIPMemString.

[cecille]

Problem

I wanted to add something in CHIPMemString and noticed that we didn't have any tests currently.

Change overview

Add tests for functionality currently in CHIPMemString.

Testing

Added new unit tests and nothing else. Verified that the new tests are running by forcing a failure.

[github-actions]

Size increase report for "esp32-example-build" from eda07d5

File	Section	File	VM
chip-lock-app.elf	.flash.text	60	60
chip-temperature-measurement-app.elf	.flash.text	32	32

Full report output

BLOAT REPORT

Files found only in the build output:
    report.csv

Comparing ./master_artifact/chip-all-clusters-app.elf and ./pull_artifact/chip-all-clusters-app.elf:

sections,vmsize,filesize

Comparing ./master_artifact/chip-pigweed-app.elf and ./pull_artifact/chip-pigweed-app.elf:

sections,vmsize,filesize

Comparing ./master_artifact/chip-persistent-storage.elf and ./pull_artifact/chip-persistent-storage.elf:

sections,vmsize,filesize

Comparing ./master_artifact/chip-ipv6only-app.elf and ./pull_artifact/chip-ipv6only-app.elf:

sections,vmsize,filesize

Comparing ./master_artifact/chip-shell.elf and ./pull_artifact/chip-shell.elf:

sections,vmsize,filesize

Comparing ./master_artifact/chip-bridge-app.elf and ./pull_artifact/chip-bridge-app.elf:

sections,vmsize,filesize

Comparing ./master_artifact/chip-lock-app.elf and ./pull_artifact/chip-lock-app.elf:

sections,vmsize,filesize
.flash.text,60,60
.debug_loc,0,-4
.xt.lit._ZNK4chip4SpanIhE7SubSpanEjj,0,-8
.xt.prop._ZNK4chip4SpanIhE7SubSpanEjj,0,-12
[Unmapped],0,-60

Comparing ./master_artifact/chip-temperature-measurement-app.elf and ./pull_artifact/chip-temperature-measurement-app.elf:

sections,vmsize,filesize
.flash.text,32,32
[Unmapped],0,-32