Add some better memory safety in discovery controller code.

[bzbarsky-apple]

Instead of assuming that subclasses give us a buffer of size at least CHIP_DEVICE_CONFIG_MAX_DISCOVERED_NODES, just enforce that via the type system.

Also switch to ranged for loops over the resulting buffers.

The changes to Span.h are for two reasons:

1. To support ranged for over a FixedSpan.
2. To disallow constructing a FixedSpan from a buffer known to be too small.

Problem

Code makes assumptions about buffer sizes that are not enforced.

Change overview

Enforce assumptions through type system.

Testing

Compiles and passes CI. Should be no behavior changes.

[github-actions]

Size increase report for "esp32-example-build" from 0e19e0d

File	Section	File	VM
chip-temperature-measurement-app.elf	.flash.text	60	60
chip-all-clusters-app.elf	.flash.text	-24	-24
chip-lock-app.elf	.flash.text	64	64
chip-shell.elf	.flash.text	4	4

Full report output

BLOAT REPORT

Files found only in the build output:
    report.csv

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

sections,vmsize,filesize

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

sections,vmsize,filesize
.debug_info,0,17163
.debug_str,0,890
.flash.text,60,60
.debug_abbrev,0,48
.debug_loc,0,-3
.debug_line,0,-6
[Unmapped],0,-60

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

sections,vmsize,filesize
.debug_info,0,24093
.debug_str,0,886
.xt.prop._ZN4chip6System5Mutex6UnlockEv,0,108
.debug_abbrev,0,48
.xt.lit._ZN4chip11DeviceLayer8Internal35GenericPlatformManagerImpl_FreeRTOSINS0_19PlatformManagerImplEE14_LockChipStackEv,0,48
.xt.lit._ZN4chip11DeviceLayer8Internal35GenericPlatformManagerImpl_FreeRTOSINS0_19PlatformManagerImplEE15_StartChipTimerEj,0,48
.xt.lit._ZN4chip11DeviceLayer8Internal35GenericPlatformManagerImpl_FreeRTOSINS0_19PlatformManagerImplEE16_UnlockChipStackEv,0,48
[Unmapped],0,24
.xt.prop._ZN4chip11DeviceLayer8Internal35GenericPlatformManagerImpl_FreeRTOSINS0_19PlatformManagerImplEE14_LockChipStackEv,0,12
.xt.prop._ZN4chip11DeviceLayer8Internal35GenericPlatformManagerImpl_FreeRTOSINS0_19PlatformManagerImplEE15_StartChipTimerEj,0,12
.xt.prop._ZN4chip11DeviceLayer8Internal35GenericPlatformManagerImpl_FreeRTOSINS0_19PlatformManagerImplEE16_UnlockChipStackEv,0,12
.debug_line,0,-6
.flash.text,-24,-24
.debug_loc,0,-29
.xt.prop._ZN4chip11DeviceLayer8Internal26GenericPlatformManagerImplINS0_19PlatformManagerImplEE14_InitChipStackEv,0,-40
.xt.lit._ZN4chip11DeviceLayer8Internal35GenericPlatformManagerImpl_FreeRTOSINS0_19PlatformManagerImplEE10_PostEventEPKNS0_15ChipDeviceEventE,0,-80
.xt.lit._ZN4chip6System5Mutex6UnlockEv,0,-128

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

sections,vmsize,filesize
.debug_info,0,24091
.debug_str,0,890
.flash.text,64,64
.debug_abbrev,0,48
.debug_loc,0,5
.debug_line,0,-6
[Unmapped],0,-64

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

sections,vmsize,filesize

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

sections,vmsize,filesize
.debug_info,0,4160
.debug_str,0,600
.flash.text,4,4
[Unmapped],0,-4