TLV reader: Fix float support and remove union UB

[anqid-g]

1. For some reason the Get(float&) signature was declared in the .h file
   but never defined. Define it as well, extracting a helper function
   for both Get(float&) and Get(double&).
2. It is undefined behaviour to use unions for type-punning in C++. Use
   raw memcpy calls instead, which is well-defined (std::bit_cast is not
   available). Compilers will generally be able to optimize this away
   unless a freestanding implementation (with possibly non-standard
   memcpy) is used.

Problem

Various improvements to TLVReader floating point code.

Change overview

1. Implement TLVReader::Get(float&)
2. Use memcpy instead of type-punning for bit conversions from integer to floating-point

Testing

• Updated TLVReader tests by copy-pasting the existing test cases for double

[CLAassistant]

All committers have signed the CLA.

[github-actions]

Size increase report for "esp32-example-build" from af1cc26

File	Section	File	VM
chip-lock-app.elf	.flash.text	68	68

Full report output

BLOAT REPORT

Files found only in the build output:
    report.csv

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

sections,vmsize,filesize
.debug_loc,0,377
.debug_info,0,199
.debug_ranges,0,64
.debug_str,0,59
.debug_line,0,58
.debug_abbrev,0,48
.debug_frame,0,40
.debug_aranges,0,8
.riscv.attributes,0,-1

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

sections,vmsize,filesize
.debug_loc,0,268
.debug_info,0,212
.debug_line,0,92
.debug_ranges,0,64
.debug_str,0,60
.debug_abbrev,0,48
.debug_frame,0,24
.debug_aranges,0,8

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

sections,vmsize,filesize
.debug_info,0,209
.debug_loc,0,175
.debug_line,0,84
.flash.text,68,68
.debug_ranges,0,56
.debug_str,0,56
.debug_abbrev,0,48
.debug_frame,0,24
.debug_aranges,0,8
[Unmapped],0,-68

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

sections,vmsize,filesize

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

sections,vmsize,filesize

[bzbarsky-apple]

Beautiful, thank you!

[bzbarsky-apple]

/rebase